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 $85.65   11.201%   $95.2437   $95.24   $95.25   $95.20  
  Purchase #2 $117.99   9.741%   $129.4834   $129.48   $129.50   $129.50  
  Purchase #3 $184.62   4.684%   $193.2676   $193.27   $193.25   $193.30  
  Purchase #4 $76.79   5.509%   $81.0204   $81.02   $81.00   $81.00  
  Purchase #5 $133.80   4.858%   $140.3   $140.30   $140.30   $140.30  
  Purchase #6 $238.71   13.414%   $270.7306   $270.73   $270.75   $270.70  
  Purchase #7 $87.55   12.319%   $98.3353   $98.34   $98.35   $98.30  
  7 purchase totals = $925.11       $1,008.3810   $1,008.38   $1,008.40   $1,008.30