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 $188.92   6.418%   $201.0449   $201.04   $201.05   $201.00  
  Purchase #2 $166.93   3.435%   $172.664   $172.66   $172.65   $172.70  
  Purchase #3 $44.53   8.663%   $48.3876   $48.39   $48.40   $48.40  
  Purchase #4 $51.98   10.707%   $57.5455   $57.55   $57.55   $57.50  
  Purchase #5 $150.80   11.388%   $167.9731   $167.97   $167.95   $168.00  
  Purchase #6 $58.92   6.352%   $62.6626   $62.66   $62.65   $62.70  
  Purchase #7 $238.59   9.418%   $261.0604   $261.06   $261.05   $261.10  
  7 purchase totals = $900.67       $971.3381   $971.33   $971.30   $971.40