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 $58.87   11.199%   $65.4629   $65.46   $65.45   $65.50  
  Purchase #2 $66.78   6.195%   $70.917   $70.92   $70.90   $70.90  
  Purchase #3 $206.79   8.580%   $224.5326   $224.53   $224.55   $224.50  
  Purchase #4 $204.65   7.420%   $219.835   $219.84   $219.85   $219.80  
  Purchase #5 $71.99   6.392%   $76.5916   $76.59   $76.60   $76.60  
  Purchase #6 $95.40   9.680%   $104.6347   $104.63   $104.65   $104.60  
  Purchase #7 $196.66   5.636%   $207.7438   $207.74   $207.75   $207.70  
  7 purchase totals = $901.14       $969.7176   $969.71   $969.75   $969.60