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	$105.78	9.836%	$116.1845	$116.18	$116.20	$116.20
Purchase #2	$92.93	11.390%	$103.5147	$103.51	$103.50	$103.50
Purchase #3	$55.28	7.614%	$59.489	$59.49	$59.50	$59.50
Purchase #4	$69.41	9.411%	$75.9422	$75.94	$75.95	$75.90
Purchase #5	$115.36	12.376%	$129.637	$129.64	$129.65	$129.60
Purchase #6	$51.26	4.232%	$53.4293	$53.43	$53.45	$53.40
Purchase #7	$34.38	8.740%	$37.3848	$37.38	$37.40	$37.40
7 purchase totals =	$524.40		$575.5815	$575.57	$575.65	$575.50