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 $174.39   5.291%   $183.617   $183.62   $183.60   $183.60  
  Purchase #2 $241.43   6.690%   $257.5817   $257.58   $257.60   $257.60  
  Purchase #3 $64.49   11.224%   $71.7284   $71.73   $71.75   $71.70  
  Purchase #4 $108.76   10.867%   $120.5789   $120.58   $120.60   $120.60  
  Purchase #5 $234.31   3.655%   $242.874   $242.87   $242.85   $242.90  
  Purchase #6 $76.87   5.448%   $81.0579   $81.06   $81.05   $81.10  
  Purchase #7 $84.92   10.828%   $94.1151   $94.12   $94.10   $94.10  
  7 purchase totals = $985.17       $1,051.5530   $1,051.56   $1,051.55   $1,051.60