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 $229.74   10.554%   $253.9868   $253.99   $254.00   $254.00  
  Purchase #2 $69.47   8.380%   $75.2916   $75.29   $75.30   $75.30  
  Purchase #3 $161.96   3.336%   $167.363   $167.36   $167.35   $167.40  
  Purchase #4 $212.80   12.382%   $239.1489   $239.15   $239.15   $239.10  
  Purchase #5 $193.55   10.189%   $213.2708   $213.27   $213.25   $213.30  
  Purchase #6 $235.46   5.870%   $249.2815   $249.28   $249.30   $249.30  
  Purchase #7 $43.98   12.749%   $49.587   $49.59   $49.60   $49.60  
  7 purchase totals = $1,146.96       $1,247.9296   $1,247.93   $1,247.95   $1,248.00