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 $69.26   6.214%   $73.5638   $73.56   $73.55   $73.60  
  Purchase #2 $188.33   13.340%   $213.4532   $213.45   $213.45   $213.50  
  Purchase #3 $83.32   13.557%   $94.6157   $94.62   $94.60   $94.60  
  Purchase #4 $61.44   13.310%   $69.6177   $69.62   $69.60   $69.60  
  Purchase #5 $240.28   8.485%   $260.6678   $260.67   $260.65   $260.70  
  Purchase #6 $188.71   9.312%   $206.2827   $206.28   $206.30   $206.30  
  Purchase #7 $35.35   12.703%   $39.8405   $39.84   $39.85   $39.80  
  7 purchase totals = $866.69       $958.0414   $958.04   $958.00   $958.10