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 $55.63   5.444%   $58.6585   $58.66   $58.65   $58.70  
  Purchase #2 $59.57   8.865%   $64.8509   $64.85   $64.85   $64.90  
  Purchase #3 $95.56   3.355%   $98.766   $98.77   $98.75   $98.80  
  Purchase #4 $135.66   9.379%   $148.3836   $148.38   $148.40   $148.40  
  Purchase #5 $46.76   10.238%   $51.5473   $51.55   $51.55   $51.50  
  Purchase #6 $155.61   8.450%   $168.759   $168.76   $168.75   $168.80  
  Purchase #7 $204.36   5.143%   $214.8702   $214.87   $214.85   $214.90  
  7 purchase totals = $753.15       $805.8355   $805.84   $805.80   $806.00