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	$30.57	11.449%	$34.07	$34.07	$34.05	$34.10
Purchase #2	$83.40	3.448%	$86.2756	$86.28	$86.30	$86.30
Purchase #3	$190.54	12.634%	$214.6128	$214.61	$214.60	$214.60
Purchase #4	$40.51	12.864%	$45.7212	$45.72	$45.70	$45.70
Purchase #5	$222.69	12.634%	$250.8247	$250.82	$250.80	$250.80
Purchase #6	$185.98	11.330%	$207.0515	$207.05	$207.05	$207.10
Purchase #7	$59.55	4.134%	$62.0118	$62.01	$62.00	$62.00
7 purchase totals =	$813.24		$900.5676	$900.56	$900.50	$900.60