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	$35.41	8.212%	$38.3179	$38.32	$38.30	$38.30
Purchase #2	$230.79	10.657%	$255.3853	$255.39	$255.40	$255.40
Purchase #3	$114.77	7.381%	$123.2412	$123.24	$123.25	$123.20
Purchase #4	$225.36	9.378%	$246.4943	$246.49	$246.50	$246.50
Purchase #5	$144.58	4.593%	$151.2206	$151.22	$151.20	$151.20
Purchase #6	$55.65	6.793%	$59.4303	$59.43	$59.45	$59.40
Purchase #7	$19.81	13.812%	$22.5462	$22.55	$22.55	$22.50
7 purchase totals =	$826.37		$896.6358	$896.64	$896.65	$896.50