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 $93.98   11.321%   $104.6195   $104.62   $104.60   $104.60  
  Purchase #2 $86.88   5.208%   $91.4047   $91.40   $91.40   $91.40  
  Purchase #3 $162.99   6.614%   $173.7702   $173.77   $173.75   $173.80  
  Purchase #4 $48.59   11.837%   $54.3416   $54.34   $54.35   $54.30  
  Purchase #5 $32.74   10.696%   $36.2419   $36.24   $36.25   $36.20  
  Purchase #6 $87.57   8.787%   $95.2648   $95.26   $95.25   $95.30  
  Purchase #7 $50.54   11.387%   $56.295   $56.30   $56.30   $56.30  
  7 purchase totals = $563.29       $611.9377   $611.93   $611.90   $611.90