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 $83.99   10.437%   $92.756   $92.76   $92.75   $92.80  
  Purchase #2 $73.35   11.794%   $82.0009   $82.00   $82.00   $82.00  
  Purchase #3 $213.42   8.398%   $231.343   $231.34   $231.35   $231.30  
  Purchase #4 $183.71   11.487%   $204.8128   $204.81   $204.80   $204.80  
  Purchase #5 $47.50   13.549%   $53.9358   $53.94   $53.95   $53.90  
  Purchase #6 $114.71   13.484%   $130.1775   $130.18   $130.20   $130.20  
  Purchase #7 $146.98   6.684%   $156.8041   $156.80   $156.80   $156.80  
  7 purchase totals = $863.66       $951.8301   $951.83   $951.85   $951.80