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 $226.45   12.769%   $255.3654   $255.37   $255.35   $255.40  
  Purchase #2 $53.99   4.840%   $56.6031   $56.60   $56.60   $56.60  
  Purchase #3 $143.47   9.161%   $156.6133   $156.61   $156.60   $156.60  
  Purchase #4 $60.73   10.697%   $67.2263   $67.23   $67.25   $67.20  
  Purchase #5 $203.98   10.719%   $225.8446   $225.84   $225.85   $225.80  
  Purchase #6 $8.39   13.660%   $9.5361   $9.54   $9.55   $9.50  
  Purchase #7 $150.66   6.814%   $160.926   $160.93   $160.95   $160.90  
  7 purchase totals = $847.67       $932.1148   $932.12   $932.15   $932.00