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 $191.93   9.740%   $210.624   $210.62   $210.60   $210.60  
  Purchase #2 $18.35   11.165%   $20.3988   $20.40   $20.40   $20.40  
  Purchase #3 $204.92   4.779%   $214.7131   $214.71   $214.70   $214.70  
  Purchase #4 $99.56   3.288%   $102.8335   $102.83   $102.85   $102.80  
  Purchase #5 $73.91   10.539%   $81.6994   $81.70   $81.70   $81.70  
  Purchase #6 $44.63   5.233%   $46.9655   $46.97   $46.95   $47.00  
  Purchase #7 $189.61   4.328%   $197.8163   $197.82   $197.80   $197.80  
  7 purchase totals = $822.91       $875.0506   $875.05   $875.00   $875.00