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 $241.78   8.387%   $262.0581   $262.06   $262.05   $262.10  
  Purchase #2 $172.51   12.256%   $193.6528   $193.65   $193.65   $193.70  
  Purchase #3 $21.78   13.417%   $24.7022   $24.70   $24.70   $24.70  
  Purchase #4 $64.85   8.726%   $70.5088   $70.51   $70.50   $70.50  
  Purchase #5 $209.29   4.158%   $217.9923   $217.99   $218.00   $218.00  
  Purchase #6 $183.63   5.389%   $193.5258   $193.53   $193.55   $193.50  
  Purchase #7 $99.73   11.160%   $110.8599   $110.86   $110.85   $110.90  
  7 purchase totals = $993.57       $1,073.2999   $1,073.30   $1,073.30   $1,073.40