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 $32.70   4.766%   $34.2585   $34.26   $34.25   $34.30  
  Purchase #2 $239.83   8.301%   $259.7383   $259.74   $259.75   $259.70  
  Purchase #3 $161.41   7.355%   $173.2817   $173.28   $173.30   $173.30  
  Purchase #4 $178.50   7.527%   $191.9357   $191.94   $191.95   $191.90  
  Purchase #5 $216.77   11.202%   $241.0526   $241.05   $241.05   $241.10  
  Purchase #6 $151.97   7.367%   $163.1656   $163.17   $163.15   $163.20  
  Purchase #7 $62.82   8.124%   $67.9235   $67.92   $67.90   $67.90  
  7 purchase totals = $1,044.00       $1,131.3559   $1,131.36   $1,131.35   $1,131.40