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 $217.94   8.569%   $236.6153   $236.62   $236.60   $236.60  
  Purchase #2 $87.30   5.370%   $91.988   $91.99   $92.00   $92.00  
  Purchase #3 $86.37   13.731%   $98.2295   $98.23   $98.25   $98.20  
  Purchase #4 $55.29   6.440%   $58.8507   $58.85   $58.85   $58.90  
  Purchase #5 $61.28   11.117%   $68.0925   $68.09   $68.10   $68.10  
  Purchase #6 $176.95   10.778%   $196.0217   $196.02   $196.00   $196.00  
  Purchase #7 $11.51   7.778%   $12.4052   $12.41   $12.40   $12.40  
  7 purchase totals = $696.64       $762.2029   $762.21   $762.20   $762.20