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	$46.91	13.435%	$53.2124	$53.21	$53.20	$53.20
Purchase #2	$160.52	12.468%	$180.5336	$180.53	$180.55	$180.50
Purchase #3	$92.81	11.442%	$103.4293	$103.43	$103.45	$103.40
Purchase #4	$196.84	3.263%	$203.2629	$203.26	$203.25	$203.30
Purchase #5	$25.54	7.621%	$27.4864	$27.49	$27.50	$27.50
Purchase #6	$65.30	13.332%	$74.0058	$74.01	$74.00	$74.00
Purchase #7	$24.83	3.477%	$25.6933	$25.69	$25.70	$25.70
7 purchase totals =	$612.75		$667.6237	$667.62	$667.65	$667.60