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 $132.99   9.825%   $146.0563   $146.06   $146.05   $146.10  
  Purchase #2 $23.83   3.619%   $24.6924   $24.69   $24.70   $24.70  
  Purchase #3 $116.53   6.718%   $124.3585   $124.36   $124.35   $124.40  
  Purchase #4 $99.31   3.403%   $102.6895   $102.69   $102.70   $102.70  
  Purchase #5 $129.57   10.829%   $143.6011   $143.60   $143.60   $143.60  
  Purchase #6 $47.43   4.435%   $49.5335   $49.53   $49.55   $49.50  
  Purchase #7 $244.76   3.382%   $253.0378   $253.04   $253.05   $253.00  
  7 purchase totals = $794.42       $843.9691   $843.97   $844.00   $844.00