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 $249.99   13.297%   $283.2312   $283.23   $283.25   $283.20  
  Purchase #2 $101.90   5.228%   $107.2273   $107.23   $107.25   $107.20  
  Purchase #3 $127.42   5.694%   $134.6753   $134.68   $134.70   $134.70  
  Purchase #4 $219.40   11.463%   $244.5498   $244.55   $244.55   $244.50  
  Purchase #5 $32.80   4.287%   $34.2061   $34.21   $34.20   $34.20  
  Purchase #6 $49.41   13.235%   $55.9494   $55.95   $55.95   $55.90  
  Purchase #7 $185.86   8.721%   $202.0689   $202.07   $202.05   $202.10  
  7 purchase totals = $966.78       $1,061.9080   $1,061.92   $1,061.95   $1,061.80