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 $76.46   8.564%   $83.008   $83.01   $83.00   $83.00  
  Purchase #2 $95.85   6.181%   $101.7745   $101.77   $101.75   $101.80  
  Purchase #3 $54.32   11.480%   $60.5559   $60.56   $60.55   $60.60  
  Purchase #4 $76.79   8.751%   $83.5099   $83.51   $83.50   $83.50  
  Purchase #5 $135.59   5.443%   $142.9702   $142.97   $142.95   $143.00  
  Purchase #6 $84.36   4.449%   $88.1132   $88.11   $88.10   $88.10  
  Purchase #7 $172.52   4.825%   $180.8441   $180.84   $180.85   $180.80  
  7 purchase totals = $695.89       $740.7758   $740.77   $740.70   $740.80