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 $226.73   11.581%   $252.9876   $252.99   $253.00   $253.00  
  Purchase #2 $75.30   9.228%   $82.2487   $82.25   $82.25   $82.20  
  Purchase #3 $89.29   6.128%   $94.7617   $94.76   $94.75   $94.80  
  Purchase #4 $11.69   12.717%   $13.1766   $13.18   $13.20   $13.20  
  Purchase #5 $182.47   12.169%   $204.6748   $204.67   $204.65   $204.70  
  Purchase #6 $166.40   9.441%   $182.1098   $182.11   $182.10   $182.10  
  Purchase #7 $57.78   11.718%   $64.5507   $64.55   $64.55   $64.60  
  7 purchase totals = $809.66       $894.5099   $894.51   $894.50   $894.60