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 $170.61   13.297%   $193.296   $193.30   $193.30   $193.30  
  Purchase #2 $178.82   11.826%   $199.9673   $199.97   $199.95   $200.00  
  Purchase #3 $59.46   6.596%   $63.382   $63.38   $63.40   $63.40  
  Purchase #4 $243.60   7.104%   $260.9053   $260.91   $260.90   $260.90  
  Purchase #5 $47.76   10.329%   $52.6931   $52.69   $52.70   $52.70  
  Purchase #6 $43.53   6.211%   $46.2336   $46.23   $46.25   $46.20  
  Purchase #7 $158.42   12.628%   $178.4253   $178.43   $178.45   $178.40  
  7 purchase totals = $902.20       $994.9026   $994.91   $994.95   $994.90