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 $96.91   6.809%   $103.5086   $103.51   $103.50   $103.50  
  Purchase #2 $53.96   4.163%   $56.2064   $56.21   $56.20   $56.20  
  Purchase #3 $178.99   8.462%   $194.1361   $194.14   $194.15   $194.10  
  Purchase #4 $93.41   9.146%   $101.9533   $101.95   $101.95   $102.00  
  Purchase #5 $55.53   7.862%   $59.8958   $59.90   $59.90   $59.90  
  Purchase #6 $215.93   6.419%   $229.7905   $229.79   $229.80   $229.80  
  Purchase #7 $9.83   9.721%   $10.7856   $10.79   $10.80   $10.80  
  7 purchase totals = $704.56       $756.2763   $756.29   $756.30   $756.30