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 $23.42   3.106%   $24.1474   $24.15   $24.15   $24.10  
  Purchase #2 $77.99   11.166%   $86.6984   $86.70   $86.70   $86.70  
  Purchase #3 $185.74   10.396%   $205.0495   $205.05   $205.05   $205.00  
  Purchase #4 $171.49   13.305%   $194.3067   $194.31   $194.30   $194.30  
  Purchase #5 $91.63   6.867%   $97.9222   $97.92   $97.90   $97.90  
  Purchase #6 $46.26   8.372%   $50.1329   $50.13   $50.15   $50.10  
  Purchase #7 $177.46   13.553%   $201.5112   $201.51   $201.50   $201.50  
  7 purchase totals = $773.99       $859.7683   $859.77   $859.75   $859.60