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 $71.29   8.159%   $77.1066   $77.11   $77.10   $77.10  
  Purchase #2 $214.93   12.661%   $242.1423   $242.14   $242.15   $242.10  
  Purchase #3 $62.69   5.462%   $66.1141   $66.11   $66.10   $66.10  
  Purchase #4 $218.36   11.111%   $242.622   $242.62   $242.60   $242.60  
  Purchase #5 $112.97   7.295%   $121.2112   $121.21   $121.20   $121.20  
  Purchase #6 $146.45   5.585%   $154.6292   $154.63   $154.65   $154.60  
  Purchase #7 $130.84   7.302%   $140.3939   $140.39   $140.40   $140.40  
  7 purchase totals = $957.53       $1,044.2193   $1,044.21   $1,044.20   $1,044.10