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 $60.73   8.297%   $65.7688   $65.77   $65.75   $65.80  
  Purchase #2 $202.85   13.755%   $230.752   $230.75   $230.75   $230.80  
  Purchase #3 $200.38   11.532%   $223.4878   $223.49   $223.50   $223.50  
  Purchase #4 $128.87   8.662%   $140.0327   $140.03   $140.05   $140.00  
  Purchase #5 $58.99   6.788%   $62.9942   $62.99   $63.00   $63.00  
  Purchase #6 $57.44   4.757%   $60.1724   $60.17   $60.15   $60.20  
  Purchase #7 $217.83   10.433%   $240.5562   $240.56   $240.55   $240.60  
  7 purchase totals = $927.09       $1,023.7641   $1,023.76   $1,023.75   $1,023.90