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	$42.90	5.831%	$45.4015	$45.40	$45.40	$45.40
Purchase #2	$185.27	12.531%	$208.4862	$208.49	$208.50	$208.50
Purchase #3	$138.46	11.550%	$154.4521	$154.45	$154.45	$154.50
Purchase #4	$67.65	5.371%	$71.2835	$71.28	$71.30	$71.30
Purchase #5	$88.65	3.861%	$92.0728	$92.07	$92.05	$92.10
Purchase #6	$245.90	3.533%	$254.5876	$254.59	$254.60	$254.60
Purchase #7	$67.63	7.864%	$72.9484	$72.95	$72.95	$72.90
7 purchase totals =	$836.46		$899.2321	$899.23	$899.25	$899.30