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 $146.28   11.285%   $162.7877   $162.79   $162.80   $162.80  
  Purchase #2 $22.89   3.197%   $23.6218   $23.62   $23.60   $23.60  
  Purchase #3 $158.90   4.800%   $166.5272   $166.53   $166.55   $166.50  
  Purchase #4 $243.89   6.428%   $259.5672   $259.57   $259.55   $259.60  
  Purchase #5 $95.94   6.182%   $101.871   $101.87   $101.85   $101.90  
  Purchase #6 $110.77   9.373%   $121.1525   $121.15   $121.15   $121.20  
  Purchase #7 $204.39   5.698%   $216.0361   $216.04   $216.05   $216.00  
  7 purchase totals = $983.06       $1,051.5635   $1,051.57   $1,051.55   $1,051.60