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 $86.78   9.391%   $94.9295   $94.93   $94.95   $94.90  
  Purchase #2 $177.77   11.316%   $197.8865   $197.89   $197.90   $197.90  
  Purchase #3 $203.35   5.721%   $214.9837   $214.98   $215.00   $215.00  
  Purchase #4 $36.93   9.551%   $40.4572   $40.46   $40.45   $40.50  
  Purchase #5 $146.76   13.158%   $166.0707   $166.07   $166.05   $166.10  
  Purchase #6 $54.51   11.649%   $60.8599   $60.86   $60.85   $60.90  
  Purchase #7 $197.79   3.141%   $204.0026   $204.00   $204.00   $204.00  
  7 purchase totals = $903.89       $979.1901   $979.19   $979.20   $979.30