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 $87.36   8.569%   $94.8459   $94.85   $94.85   $94.80  
  Purchase #2 $43.62   6.680%   $46.5338   $46.53   $46.55   $46.50  
  Purchase #3 $219.92   4.202%   $229.161   $229.16   $229.15   $229.20  
  Purchase #4 $37.38   6.685%   $39.8789   $39.88   $39.90   $39.90  
  Purchase #5 $215.78   13.141%   $244.1356   $244.14   $244.15   $244.10  
  Purchase #6 $138.99   11.143%   $154.4777   $154.48   $154.50   $154.50  
  Purchase #7 $88.69   7.219%   $95.0925   $95.09   $95.10   $95.10  
  7 purchase totals = $831.74       $904.1254   $904.13   $904.20   $904.10