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 $247.69   3.205%   $255.6285   $255.63   $255.65   $255.60  
  Purchase #2 $126.39   4.278%   $131.797   $131.80   $131.80   $131.80  
  Purchase #3 $41.60   3.851%   $43.202   $43.20   $43.20   $43.20  
  Purchase #4 $89.25   3.389%   $92.2747   $92.27   $92.25   $92.30  
  Purchase #5 $229.50   11.663%   $256.2666   $256.27   $256.25   $256.30  
  Purchase #6 $175.41   12.569%   $197.4573   $197.46   $197.45   $197.50  
  Purchase #7 $65.91   3.221%   $68.033   $68.03   $68.05   $68.00  
  7 purchase totals = $975.75       $1,044.6591   $1,044.66   $1,044.65   $1,044.70