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 $130.38   13.614%   $148.1299   $148.13   $148.15   $148.10  
  Purchase #2 $113.94   4.305%   $118.8451   $118.85   $118.85   $118.80  
  Purchase #3 $53.41   9.656%   $58.5673   $58.57   $58.55   $58.60  
  Purchase #4 $247.41   13.420%   $280.6124   $280.61   $280.60   $280.60  
  Purchase #5 $188.62   11.585%   $210.4716   $210.47   $210.45   $210.50  
  Purchase #6 $5.49   9.804%   $6.0282   $6.03   $6.05   $6.00  
  Purchase #7 $216.37   4.864%   $226.8942   $226.89   $226.90   $226.90  
  7 purchase totals = $955.62       $1,049.5487   $1,049.55   $1,049.55   $1,049.50