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 $67.39   13.276%   $76.3367   $76.34   $76.35   $76.30  
  Purchase #2 $199.65   5.340%   $210.3113   $210.31   $210.30   $210.30  
  Purchase #3 $117.27   12.639%   $132.0918   $132.09   $132.10   $132.10  
  Purchase #4 $225.71   8.450%   $244.7825   $244.78   $244.80   $244.80  
  Purchase #5 $168.89   12.781%   $190.4758   $190.48   $190.50   $190.50  
  Purchase #6 $127.49   3.709%   $132.2186   $132.22   $132.20   $132.20  
  Purchase #7 $219.30   10.561%   $242.4603   $242.46   $242.45   $242.50  
  7 purchase totals = $1,125.70       $1,228.6770   $1,228.68   $1,228.70   $1,228.70