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 $193.85   8.863%   $211.0309   $211.03   $211.05   $211.00  
  Purchase #2 $9.37   9.756%   $10.2841   $10.28   $10.30   $10.30  
  Purchase #3 $17.60   8.164%   $19.0369   $19.04   $19.05   $19.00  
  Purchase #4 $133.44   4.511%   $139.4595   $139.46   $139.45   $139.50  
  Purchase #5 $167.56   12.429%   $188.386   $188.39   $188.40   $188.40  
  Purchase #6 $65.70   8.575%   $71.3338   $71.33   $71.35   $71.30  
  Purchase #7 $118.97   9.338%   $130.0794   $130.08   $130.10   $130.10  
  7 purchase totals = $706.49       $769.6106   $769.61   $769.70   $769.60