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 $204.84   6.394%   $217.9375   $217.94   $217.95   $217.90  
  Purchase #2 $189.95   10.341%   $209.5927   $209.59   $209.60   $209.60  
  Purchase #3 $130.64   11.605%   $145.8008   $145.80   $145.80   $145.80  
  Purchase #4 $77.54   5.674%   $81.9396   $81.94   $81.95   $81.90  
  Purchase #5 $14.35   6.756%   $15.3195   $15.32   $15.30   $15.30  
  Purchase #6 $60.64   6.863%   $64.8017   $64.80   $64.80   $64.80  
  Purchase #7 $74.93   8.715%   $81.4601   $81.46   $81.45   $81.50  
  7 purchase totals = $752.89       $816.8519   $816.85   $816.85   $816.80