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 $115.65   8.257%   $125.1992   $125.20   $125.20   $125.20  
  Purchase #2 $164.72   5.543%   $173.8504   $173.85   $173.85   $173.90  
  Purchase #3 $51.35   13.311%   $58.1852   $58.19   $58.20   $58.20  
  Purchase #4 $222.73   6.120%   $236.3611   $236.36   $236.35   $236.40  
  Purchase #5 $178.27   8.574%   $193.5549   $193.55   $193.55   $193.60  
  Purchase #6 $71.64   13.477%   $81.2949   $81.29   $81.30   $81.30  
  Purchase #7 $54.35   9.465%   $59.4942   $59.49   $59.50   $59.50  
  7 purchase totals = $858.71       $927.9399   $927.93   $927.95   $928.10