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	$98.65	13.392%	$111.8612	$111.86	$111.85	$111.90
Purchase #2	$170.93	10.847%	$189.4708	$189.47	$189.45	$189.50
Purchase #3	$108.52	3.338%	$112.1424	$112.14	$112.15	$112.10
Purchase #4	$183.25	4.617%	$191.7107	$191.71	$191.70	$191.70
Purchase #5	$104.91	4.623%	$109.76	$109.76	$109.75	$109.80
Purchase #6	$53.59	3.394%	$55.4088	$55.41	$55.40	$55.40
Purchase #7	$125.35	4.132%	$130.5295	$130.53	$130.55	$130.50
7 purchase totals =	$845.20		$900.8834	$900.88	$900.85	$900.90