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 $230.53   8.315%   $249.6986   $249.70   $249.70   $249.70  
  Purchase #2 $83.59   12.669%   $94.18   $94.18   $94.20   $94.20  
  Purchase #3 $80.73   3.591%   $83.629   $83.63   $83.65   $83.60  
  Purchase #4 $140.65   6.384%   $149.6291   $149.63   $149.65   $149.60  
  Purchase #5 $231.85   4.493%   $242.267   $242.27   $242.25   $242.30  
  Purchase #6 $127.46   7.580%   $137.1215   $137.12   $137.10   $137.10  
  Purchase #7 $174.38   9.383%   $190.7421   $190.74   $190.75   $190.70  
  7 purchase totals = $1,069.19       $1,147.2673   $1,147.27   $1,147.30   $1,147.20