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 $228.66   8.111%   $247.2066   $247.21   $247.20   $247.20  
  Purchase #2 $206.50   7.223%   $221.4155   $221.42   $221.40   $221.40  
  Purchase #3 $184.83   5.540%   $195.0696   $195.07   $195.05   $195.10  
  Purchase #4 $54.35   8.694%   $59.0752   $59.08   $59.10   $59.10  
  Purchase #5 $83.37   8.208%   $90.213   $90.21   $90.20   $90.20  
  Purchase #6 $162.75   13.443%   $184.6285   $184.63   $184.65   $184.60  
  Purchase #7 $67.27   13.842%   $76.5815   $76.58   $76.60   $76.60  
  7 purchase totals = $987.73       $1,074.1899   $1,074.20   $1,074.20   $1,074.20