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 $26.74   10.740%   $29.6119   $29.61   $29.60   $29.60  
  Purchase #2 $143.73   9.339%   $157.1529   $157.15   $157.15   $157.20  
  Purchase #3 $143.54   6.331%   $152.6275   $152.63   $152.65   $152.60  
  Purchase #4 $206.29   4.141%   $214.8325   $214.83   $214.85   $214.80  
  Purchase #5 $142.41   12.826%   $160.6755   $160.68   $160.70   $160.70  
  Purchase #6 $189.58   8.654%   $205.9863   $205.99   $206.00   $206.00  
  Purchase #7 $92.70   13.239%   $104.9726   $104.97   $104.95   $105.00  
  7 purchase totals = $944.99       $1,025.8592   $1,025.86   $1,025.90   $1,025.90