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 $50.54   13.542%   $57.3841   $57.38   $57.40   $57.40  
  Purchase #2 $179.98   13.294%   $203.9065   $203.91   $203.90   $203.90  
  Purchase #3 $123.63   5.247%   $130.1169   $130.12   $130.10   $130.10  
  Purchase #4 $138.98   8.466%   $150.746   $150.75   $150.75   $150.70  
  Purchase #5 $74.89   9.519%   $82.0188   $82.02   $82.00   $82.00  
  Purchase #6 $208.91   6.376%   $222.2301   $222.23   $222.25   $222.20  
  Purchase #7 $205.43   5.733%   $217.2073   $217.21   $217.20   $217.20  
  7 purchase totals = $982.36       $1,063.6097   $1,063.62   $1,063.60   $1,063.50