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 $228.97   6.822%   $244.5903   $244.59   $244.60   $244.60  
  Purchase #2 $219.64   6.429%   $233.7607   $233.76   $233.75   $233.80  
  Purchase #3 $224.68   11.215%   $249.8779   $249.88   $249.90   $249.90  
  Purchase #4 $187.55   4.474%   $195.941   $195.94   $195.95   $195.90  
  Purchase #5 $130.49   6.664%   $139.1859   $139.19   $139.20   $139.20  
  Purchase #6 $72.72   11.755%   $81.2682   $81.27   $81.25   $81.30  
  Purchase #7 $203.36   10.779%   $225.2802   $225.28   $225.30   $225.30  
  7 purchase totals = $1,267.41       $1,369.9042   $1,369.91   $1,369.95   $1,370.00