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 $247.95   13.478%   $281.3687   $281.37   $281.35   $281.40  
  Purchase #2 $111.42   12.405%   $125.2417   $125.24   $125.25   $125.20  
  Purchase #3 $104.61   6.519%   $111.4295   $111.43   $111.45   $111.40  
  Purchase #4 $164.93   5.489%   $173.983   $173.98   $174.00   $174.00  
  Purchase #5 $146.25   8.721%   $159.0045   $159.00   $159.00   $159.00  
  Purchase #6 $83.54   11.298%   $92.9783   $92.98   $93.00   $93.00  
  Purchase #7 $56.88   10.835%   $63.0429   $63.04   $63.05   $63.00  
  7 purchase totals = $915.58       $1,007.0486   $1,007.04   $1,007.10   $1,007.00