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 $208.94   13.124%   $236.3613   $236.36   $236.35   $236.40  
  Purchase #2 $164.62   9.871%   $180.8696   $180.87   $180.85   $180.90  
  Purchase #3 $17.80   5.145%   $18.7158   $18.72   $18.70   $18.70  
  Purchase #4 $140.39   13.840%   $159.82   $159.82   $159.80   $159.80  
  Purchase #5 $190.36   12.171%   $213.5287   $213.53   $213.55   $213.50  
  Purchase #6 $14.55   5.810%   $15.3954   $15.40   $15.40   $15.40  
  Purchase #7 $246.85   3.469%   $255.4132   $255.41   $255.40   $255.40  
  7 purchase totals = $983.51       $1,080.1040   $1,080.11   $1,080.05   $1,080.10