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 $88.58   5.383%   $93.3483   $93.35   $93.35   $93.30  
  Purchase #2 $244.42   12.576%   $275.1583   $275.16   $275.15   $275.20  
  Purchase #3 $62.26   6.168%   $66.1002   $66.10   $66.10   $66.10  
  Purchase #4 $61.35   11.699%   $68.5273   $68.53   $68.55   $68.50  
  Purchase #5 $15.40   12.668%   $17.3509   $17.35   $17.35   $17.40  
  Purchase #6 $22.78   7.396%   $24.4648   $24.46   $24.45   $24.50  
  Purchase #7 $33.84   11.123%   $37.604   $37.60   $37.60   $37.60  
  7 purchase totals = $528.63       $582.5538   $582.55   $582.55   $582.60