Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $111.73   12.657%   $125.8717   $125.87   $125.85   $125.90  
  Purchase #2 $181.61   6.698%   $193.7742   $193.77   $193.75   $193.80  
  Purchase #3 $121.49   9.221%   $132.6926   $132.69   $132.70   $132.70  
  Purchase #4 $184.83   13.688%   $210.1295   $210.13   $210.15   $210.10  
  Purchase #5 $162.72   13.668%   $184.9606   $184.96   $184.95   $185.00  
  Purchase #6 $233.97   5.153%   $246.0265   $246.03   $246.05   $246.00  
  Purchase #7 $153.36   5.143%   $161.2473   $161.25   $161.25   $161.20  
  7 purchase totals = $1,149.71       $1,254.7024   $1,254.70   $1,254.70   $1,254.70