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 $224.38   9.474%   $245.6378   $245.64   $245.65   $245.60  
  Purchase #2 $118.54   13.352%   $134.3675   $134.37   $134.35   $134.40  
  Purchase #3 $246.66   13.392%   $279.6927   $279.69   $279.70   $279.70  
  Purchase #4 $198.87   5.433%   $209.6746   $209.67   $209.65   $209.70  
  Purchase #5 $94.80   8.662%   $103.0116   $103.01   $103.00   $103.00  
  Purchase #6 $166.42   9.775%   $182.6876   $182.69   $182.70   $182.70  
  Purchase #7 $166.60   5.303%   $175.4348   $175.43   $175.45   $175.40  
  7 purchase totals = $1,216.27       $1,330.5066   $1,330.50   $1,330.50   $1,330.50