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	$240.48	4.158%	$250.4792	$250.48	$250.50	$250.50
Purchase #2	$148.78	11.678%	$166.1545	$166.15	$166.15	$166.20
Purchase #3	$44.74	13.108%	$50.6045	$50.60	$50.60	$50.60
Purchase #4	$19.25	6.234%	$20.45	$20.45	$20.45	$20.50
Purchase #5	$164.26	13.331%	$186.1575	$186.16	$186.15	$186.20
Purchase #6	$166.99	11.749%	$186.6097	$186.61	$186.60	$186.60
Purchase #7	$158.57	13.235%	$179.5567	$179.56	$179.55	$179.60
7 purchase totals =	$943.07		$1,040.0121	$1,040.01	$1,040.00	$1,040.20