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 $140.52   11.437%   $156.5913   $156.59   $156.60   $156.60  
  Purchase #2 $41.63   11.542%   $46.4349   $46.43   $46.45   $46.40  
  Purchase #3 $31.67   10.487%   $34.9912   $34.99   $35.00   $35.00  
  Purchase #4 $46.26   3.669%   $47.9573   $47.96   $47.95   $48.00  
  Purchase #5 $133.73   13.674%   $152.0162   $152.02   $152.00   $152.00  
  Purchase #6 $200.98   4.173%   $209.3669   $209.37   $209.35   $209.40  
  Purchase #7 $232.72   5.287%   $245.0239   $245.02   $245.00   $245.00  
  7 purchase totals = $827.51       $892.3817   $892.38   $892.35   $892.40