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 $73.38   3.804%   $76.1714   $76.17   $76.15   $76.20  
  Purchase #2 $159.86   9.213%   $174.5879   $174.59   $174.60   $174.60  
  Purchase #3 $85.61   8.833%   $93.1719   $93.17   $93.15   $93.20  
  Purchase #4 $224.39   7.745%   $241.769   $241.77   $241.75   $241.80  
  Purchase #5 $104.49   5.355%   $110.0854   $110.09   $110.10   $110.10  
  Purchase #6 $130.72   8.111%   $141.3227   $141.32   $141.30   $141.30  
  Purchase #7 $163.33   12.205%   $183.2644   $183.26   $183.25   $183.30  
  7 purchase totals = $941.78       $1,020.3727   $1,020.37   $1,020.30   $1,020.50