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	$136.31	9.580%	$149.3685	$149.37	$149.35	$149.40
Purchase #2	$17.88	6.404%	$19.025	$19.03	$19.05	$19.00
Purchase #3	$6.58	10.161%	$7.2486	$7.25	$7.25	$7.20
Purchase #4	$88.69	13.250%	$100.4414	$100.44	$100.45	$100.40
Purchase #5	$72.54	7.182%	$77.7498	$77.75	$77.75	$77.70
Purchase #6	$205.31	8.197%	$222.1393	$222.14	$222.15	$222.10
Purchase #7	$66.48	7.862%	$71.7067	$71.71	$71.70	$71.70
7 purchase totals =	$593.79		$647.6793	$647.69	$647.70	$647.50