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 $245.37   9.400%   $268.4348   $268.43   $268.45   $268.40  
  Purchase #2 $14.68   12.860%   $16.5678   $16.57   $16.55   $16.60  
  Purchase #3 $56.29   9.216%   $61.4777   $61.48   $61.50   $61.50  
  Purchase #4 $119.84   8.366%   $129.8658   $129.87   $129.85   $129.90  
  Purchase #5 $141.66   13.189%   $160.3435   $160.34   $160.35   $160.30  
  Purchase #6 $232.88   4.472%   $243.2944   $243.29   $243.30   $243.30  
  Purchase #7 $66.45   11.243%   $73.921   $73.92   $73.90   $73.90  
  7 purchase totals = $877.17       $953.9050   $953.90   $953.90   $953.90