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 $88.39   13.650%   $100.4552   $100.46   $100.45   $100.50  
  Purchase #2 $24.41   10.348%   $26.9359   $26.94   $26.95   $26.90  
  Purchase #3 $59.71   7.690%   $64.3017   $64.30   $64.30   $64.30  
  Purchase #4 $70.56   5.460%   $74.4126   $74.41   $74.40   $74.40  
  Purchase #5 $177.98   4.846%   $186.6049   $186.60   $186.60   $186.60  
  Purchase #6 $176.90   11.368%   $197.01   $197.01   $197.00   $197.00  
  Purchase #7 $102.99   8.474%   $111.7174   $111.72   $111.70   $111.70  
  7 purchase totals = $700.94       $761.4377   $761.44   $761.40   $761.40