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 $64.77   8.387%   $70.2023   $70.20   $70.20   $70.20  
  Purchase #2 $173.34   6.312%   $184.2812   $184.28   $184.30   $184.30  
  Purchase #3 $249.99   8.832%   $272.0691   $272.07   $272.05   $272.10  
  Purchase #4 $27.96   12.275%   $31.3921   $31.39   $31.40   $31.40  
  Purchase #5 $157.31   6.872%   $168.1203   $168.12   $168.10   $168.10  
  Purchase #6 $92.49   9.391%   $101.1757   $101.18   $101.20   $101.20  
  Purchase #7 $107.64   4.734%   $112.7357   $112.74   $112.75   $112.70  
  7 purchase totals = $873.50       $939.9764   $939.98   $940.00   $940.00