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 $140.33   8.785%   $152.658   $152.66   $152.65   $152.70  
  Purchase #2 $78.74   5.863%   $83.3565   $83.36   $83.35   $83.40  
  Purchase #3 $155.80   5.201%   $163.9032   $163.90   $163.90   $163.90  
  Purchase #4 $161.71   3.584%   $167.5057   $167.51   $167.50   $167.50  
  Purchase #5 $237.90   11.766%   $265.8913   $265.89   $265.90   $265.90  
  Purchase #6 $67.41   9.674%   $73.9312   $73.93   $73.95   $73.90  
  Purchase #7 $122.88   9.215%   $134.2034   $134.20   $134.20   $134.20  
  7 purchase totals = $964.77       $1,041.4493   $1,041.45   $1,041.45   $1,041.50