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 $144.92   9.442%   $158.6033   $158.60   $158.60   $158.60  
  Purchase #2 $176.92   13.816%   $201.3633   $201.36   $201.35   $201.40  
  Purchase #3 $15.99   5.275%   $16.8335   $16.83   $16.85   $16.80  
  Purchase #4 $152.99   4.224%   $159.4523   $159.45   $159.45   $159.50  
  Purchase #5 $100.34   9.845%   $110.2185   $110.22   $110.20   $110.20  
  Purchase #6 $248.56   11.342%   $276.7517   $276.75   $276.75   $276.80  
  Purchase #7 $126.35   9.805%   $138.7386   $138.74   $138.75   $138.70  
  7 purchase totals = $966.07       $1,061.9612   $1,061.95   $1,061.95   $1,062.00