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 $87.27   8.114%   $94.3511   $94.35   $94.35   $94.40  
  Purchase #2 $85.54   11.827%   $95.6568   $95.66   $95.65   $95.70  
  Purchase #3 $97.50   12.705%   $109.8874   $109.89   $109.90   $109.90  
  Purchase #4 $220.59   4.691%   $230.9379   $230.94   $230.95   $230.90  
  Purchase #5 $75.48   12.312%   $84.7731   $84.77   $84.75   $84.80  
  Purchase #6 $209.26   13.154%   $236.7861   $236.79   $236.80   $236.80  
  Purchase #7 $98.71   4.823%   $103.4708   $103.47   $103.45   $103.50  
  7 purchase totals = $874.35       $955.8632   $955.87   $955.85   $956.00