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 $60.76   5.845%   $64.3114   $64.31   $64.30   $64.30  
  Purchase #2 $174.62   10.720%   $193.3393   $193.34   $193.35   $193.30  
  Purchase #3 $218.58   10.844%   $242.2828   $242.28   $242.30   $242.30  
  Purchase #4 $162.78   4.743%   $170.5007   $170.50   $170.50   $170.50  
  Purchase #5 $213.26   4.426%   $222.6989   $222.70   $222.70   $222.70  
  Purchase #6 $88.27   9.777%   $96.9002   $96.90   $96.90   $96.90  
  Purchase #7 $148.80   7.238%   $159.5701   $159.57   $159.55   $159.60  
  7 purchase totals = $1,067.07       $1,149.6034   $1,149.60   $1,149.60   $1,149.60