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 $241.71   11.179%   $268.7308   $268.73   $268.75   $268.70  
  Purchase #2 $65.42   10.707%   $72.4245   $72.42   $72.40   $72.40  
  Purchase #3 $119.94   7.600%   $129.0554   $129.06   $129.05   $129.10  
  Purchase #4 $77.56   9.347%   $84.8095   $84.81   $84.80   $84.80  
  Purchase #5 $202.27   12.224%   $226.9955   $227.00   $227.00   $227.00  
  Purchase #6 $67.34   5.441%   $71.004   $71.00   $71.00   $71.00  
  Purchase #7 $30.64   10.810%   $33.9522   $33.95   $33.95   $34.00  
  7 purchase totals = $804.88       $886.9719   $886.97   $886.95   $887.00