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 $55.99   10.188%   $61.6943   $61.69   $61.70   $61.70  
  Purchase #2 $217.33   13.252%   $246.1306   $246.13   $246.15   $246.10  
  Purchase #3 $24.28   6.164%   $25.7766   $25.78   $25.80   $25.80  
  Purchase #4 $185.36   8.709%   $201.503   $201.50   $201.50   $201.50  
  Purchase #5 $211.89   6.774%   $226.2434   $226.24   $226.25   $226.20  
  Purchase #6 $162.74   13.396%   $184.5407   $184.54   $184.55   $184.50  
  Purchase #7 $81.31   4.376%   $84.8681   $84.87   $84.85   $84.90  
  7 purchase totals = $938.90       $1,030.7567   $1,030.75   $1,030.80   $1,030.70