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 $104.37   3.281%   $107.7944   $107.79   $107.80   $107.80  
  Purchase #2 $136.44   11.185%   $151.7008   $151.70   $151.70   $151.70  
  Purchase #3 $140.79   5.541%   $148.5912   $148.59   $148.60   $148.60  
  Purchase #4 $58.69   6.415%   $62.455   $62.46   $62.45   $62.50  
  Purchase #5 $197.63   11.289%   $219.9405   $219.94   $219.95   $219.90  
  Purchase #6 $157.34   8.259%   $170.3347   $170.33   $170.35   $170.30  
  Purchase #7 $84.70   8.120%   $91.5776   $91.58   $91.60   $91.60  
  7 purchase totals = $879.96       $952.3942   $952.39   $952.45   $952.40