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 $22.27   11.702%   $24.876   $24.88   $24.90   $24.90  
  Purchase #2 $193.26   9.383%   $211.3936   $211.39   $211.40   $211.40  
  Purchase #3 $12.93   3.203%   $13.3441   $13.34   $13.35   $13.30  
  Purchase #4 $171.98   13.281%   $194.8207   $194.82   $194.80   $194.80  
  Purchase #5 $191.36   6.828%   $204.4261   $204.43   $204.45   $204.40  
  Purchase #6 $234.88   10.804%   $260.2564   $260.26   $260.25   $260.30  
  Purchase #7 $45.43   12.540%   $51.1269   $51.13   $51.15   $51.10  
  7 purchase totals = $872.11       $960.2438   $960.25   $960.30   $960.20