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 $212.41   6.652%   $226.5395   $226.54   $226.55   $226.50  
  Purchase #2 $53.52   9.185%   $58.4358   $58.44   $58.45   $58.40  
  Purchase #3 $57.92   4.807%   $60.7042   $60.70   $60.70   $60.70  
  Purchase #4 $125.98   5.634%   $133.0777   $133.08   $133.10   $133.10  
  Purchase #5 $178.65   5.565%   $188.5919   $188.59   $188.60   $188.60  
  Purchase #6 $49.86   3.345%   $51.5278   $51.53   $51.55   $51.50  
  Purchase #7 $70.37   11.549%   $78.497   $78.50   $78.50   $78.50  
  7 purchase totals = $748.71       $797.3739   $797.38   $797.45   $797.30