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 $166.93   11.275%   $185.7514   $185.75   $185.75   $185.80  
  Purchase #2 $65.92   11.630%   $73.5865   $73.59   $73.60   $73.60  
  Purchase #3 $7.79   10.298%   $8.5922   $8.59   $8.60   $8.60  
  Purchase #4 $61.86   6.612%   $65.9502   $65.95   $65.95   $66.00  
  Purchase #5 $34.28   3.633%   $35.5254   $35.53   $35.55   $35.50  
  Purchase #6 $216.40   7.221%   $232.0262   $232.03   $232.05   $232.00  
  Purchase #7 $150.91   4.742%   $158.0662   $158.07   $158.05   $158.10  
  7 purchase totals = $704.09       $759.4981   $759.51   $759.55   $759.60