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 $84.83   11.507%   $94.5914   $94.59   $94.60   $94.60  
  Purchase #2 $12.27   4.259%   $12.7926   $12.79   $12.80   $12.80  
  Purchase #3 $181.44   9.531%   $198.733   $198.73   $198.75   $198.70  
  Purchase #4 $188.63   5.606%   $199.2046   $199.20   $199.20   $199.20  
  Purchase #5 $163.32   7.324%   $175.2816   $175.28   $175.30   $175.30  
  Purchase #6 $64.61   11.545%   $72.0692   $72.07   $72.05   $72.10  
  Purchase #7 $240.53   11.682%   $268.6287   $268.63   $268.65   $268.60  
  7 purchase totals = $935.63       $1,021.3011   $1,021.29   $1,021.35   $1,021.30