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 $193.69   5.151%   $203.667   $203.67   $203.65   $203.70  
  Purchase #2 $49.55   9.417%   $54.2161   $54.22   $54.20   $54.20  
  Purchase #3 $153.84   9.770%   $168.8702   $168.87   $168.85   $168.90  
  Purchase #4 $124.80   6.558%   $132.9844   $132.98   $133.00   $133.00  
  Purchase #5 $95.61   4.761%   $100.162   $100.16   $100.15   $100.20  
  Purchase #6 $126.44   10.322%   $139.4911   $139.49   $139.50   $139.50  
  Purchase #7 $60.89   5.149%   $64.0252   $64.03   $64.05   $64.00  
  7 purchase totals = $804.82       $863.4160   $863.42   $863.40   $863.50