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 $50.86   8.635%   $55.2518   $55.25   $55.25   $55.30  
  Purchase #2 $92.79   9.712%   $101.8018   $101.80   $101.80   $101.80  
  Purchase #3 $179.78   12.336%   $201.9577   $201.96   $201.95   $202.00  
  Purchase #4 $126.87   4.229%   $132.2353   $132.24   $132.25   $132.20  
  Purchase #5 $118.72   5.486%   $125.233   $125.23   $125.25   $125.20  
  Purchase #6 $159.88   10.525%   $176.7074   $176.71   $176.70   $176.70  
  Purchase #7 $194.99   10.373%   $215.2163   $215.22   $215.20   $215.20  
  7 purchase totals = $923.89       $1,008.4033   $1,008.41   $1,008.40   $1,008.40