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 $229.81   6.366%   $244.4397   $244.44   $244.45   $244.40  
  Purchase #2 $184.89   13.466%   $209.7873   $209.79   $209.80   $209.80  
  Purchase #3 $178.49   5.649%   $188.5729   $188.57   $188.55   $188.60  
  Purchase #4 $225.39   3.357%   $232.9563   $232.96   $232.95   $233.00  
  Purchase #5 $150.61   13.792%   $171.3821   $171.38   $171.40   $171.40  
  Purchase #6 $236.75   4.649%   $247.7565   $247.76   $247.75   $247.80  
  Purchase #7 $58.73   5.620%   $62.0306   $62.03   $62.05   $62.00  
  7 purchase totals = $1,264.67       $1,356.9254   $1,356.93   $1,356.95   $1,357.00