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 $26.85   5.534%   $28.3359   $28.34   $28.35   $28.30  
  Purchase #2 $229.51   9.618%   $251.5843   $251.58   $251.60   $251.60  
  Purchase #3 $239.68   10.683%   $265.285   $265.29   $265.30   $265.30  
  Purchase #4 $212.51   3.868%   $220.7299   $220.73   $220.75   $220.70  
  Purchase #5 $218.36   8.103%   $236.0537   $236.05   $236.05   $236.10  
  Purchase #6 $95.43   9.291%   $104.2964   $104.30   $104.30   $104.30  
  Purchase #7 $177.62   9.656%   $194.771   $194.77   $194.75   $194.80  
  7 purchase totals = $1,199.96       $1,301.0562   $1,301.06   $1,301.10   $1,301.10