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 $152.66   8.281%   $165.3018   $165.30   $165.30   $165.30  
  Purchase #2 $242.31   5.211%   $254.9368   $254.94   $254.95   $254.90  
  Purchase #3 $195.84   5.593%   $206.7933   $206.79   $206.80   $206.80  
  Purchase #4 $184.47   7.844%   $198.9398   $198.94   $198.95   $198.90  
  Purchase #5 $146.74   7.169%   $157.2598   $157.26   $157.25   $157.30  
  Purchase #6 $166.96   3.801%   $173.3061   $173.31   $173.30   $173.30  
  Purchase #7 $177.53   9.437%   $194.2835   $194.28   $194.30   $194.30  
  7 purchase totals = $1,266.51       $1,350.8211   $1,350.82   $1,350.85   $1,350.80