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 $148.45   7.291%   $159.2735   $159.27   $159.25   $159.30  
  Purchase #2 $159.63   11.806%   $178.4759   $178.48   $178.50   $178.50  
  Purchase #3 $242.63   5.780%   $256.654   $256.65   $256.65   $256.70  
  Purchase #4 $34.28   8.646%   $37.2438   $37.24   $37.25   $37.20  
  Purchase #5 $117.48   11.850%   $131.4014   $131.40   $131.40   $131.40  
  Purchase #6 $61.44   9.536%   $67.2989   $67.30   $67.30   $67.30  
  Purchase #7 $60.37   6.475%   $64.279   $64.28   $64.30   $64.30  
  7 purchase totals = $824.28       $894.6265   $894.62   $894.65   $894.70