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 $45.84   10.413%   $50.6133   $50.61   $50.60   $50.60  
  Purchase #2 $238.85   11.793%   $267.0176   $267.02   $267.00   $267.00  
  Purchase #3 $187.91   13.695%   $213.6443   $213.64   $213.65   $213.60  
  Purchase #4 $10.53   13.430%   $11.9442   $11.94   $11.95   $11.90  
  Purchase #5 $34.87   7.873%   $37.6153   $37.62   $37.60   $37.60  
  Purchase #6 $133.54   3.311%   $137.9615   $137.96   $137.95   $138.00  
  Purchase #7 $142.50   12.671%   $160.5562   $160.56   $160.55   $160.60  
  7 purchase totals = $794.04       $879.3524   $879.35   $879.30   $879.30