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 $241.82   7.181%   $259.1851   $259.19   $259.20   $259.20  
  Purchase #2 $162.40   12.395%   $182.5295   $182.53   $182.55   $182.50  
  Purchase #3 $151.34   6.741%   $161.5418   $161.54   $161.55   $161.50  
  Purchase #4 $237.54   13.219%   $268.9404   $268.94   $268.95   $268.90  
  Purchase #5 $124.62   10.599%   $137.8285   $137.83   $137.85   $137.80  
  Purchase #6 $161.96   4.197%   $168.7575   $168.76   $168.75   $168.80  
  Purchase #7 $131.31   13.469%   $148.9961   $149.00   $149.00   $149.00  
  7 purchase totals = $1,210.99       $1,327.7789   $1,327.79   $1,327.85   $1,327.70