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 $248.65   7.625%   $267.6096   $267.61   $267.60   $267.60  
  Purchase #2 $43.71   10.197%   $48.1671   $48.17   $48.15   $48.20  
  Purchase #3 $16.93   13.561%   $19.2259   $19.23   $19.25   $19.20  
  Purchase #4 $164.84   9.471%   $180.452   $180.45   $180.45   $180.50  
  Purchase #5 $149.70   5.313%   $157.6536   $157.65   $157.65   $157.70  
  Purchase #6 $88.73   6.411%   $94.4185   $94.42   $94.40   $94.40  
  Purchase #7 $232.81   13.454%   $264.1323   $264.13   $264.15   $264.10  
  7 purchase totals = $945.37       $1,031.6590   $1,031.66   $1,031.65   $1,031.70