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 $124.96   7.522%   $134.3595   $134.36   $134.35   $134.40  
  Purchase #2 $112.71   6.463%   $119.9944   $119.99   $120.00   $120.00  
  Purchase #3 $116.71   6.385%   $124.1619   $124.16   $124.15   $124.20  
  Purchase #4 $81.98   7.569%   $88.1851   $88.19   $88.20   $88.20  
  Purchase #5 $67.43   12.398%   $75.79   $75.79   $75.80   $75.80  
  Purchase #6 $195.70   4.832%   $205.1562   $205.16   $205.15   $205.20  
  Purchase #7 $192.52   10.680%   $213.0811   $213.08   $213.10   $213.10  
  7 purchase totals = $892.01       $960.7282   $960.73   $960.75   $960.90