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	$115.80	12.395%	$130.1534	$130.15	$130.15	$130.20
Purchase #2	$164.61	9.280%	$179.8858	$179.89	$179.90	$179.90
Purchase #3	$89.32	13.364%	$101.2567	$101.26	$101.25	$101.30
Purchase #4	$113.89	9.219%	$124.3895	$124.39	$124.40	$124.40
Purchase #5	$114.58	7.620%	$123.311	$123.31	$123.30	$123.30
Purchase #6	$54.51	5.527%	$57.5228	$57.52	$57.50	$57.50
Purchase #7	$68.27	7.733%	$73.5493	$73.55	$73.55	$73.50
7 purchase totals =	$720.98		$790.0685	$790.07	$790.05	$790.10