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	$135.32	13.483%	$153.5652	$153.57	$153.55	$153.60
Purchase #2	$185.80	7.591%	$199.9041	$199.90	$199.90	$199.90
Purchase #3	$135.28	11.546%	$150.8994	$150.90	$150.90	$150.90
Purchase #4	$122.80	3.798%	$127.4639	$127.46	$127.45	$127.50
Purchase #5	$49.50	7.481%	$53.2031	$53.20	$53.20	$53.20
Purchase #6	$60.71	10.419%	$67.0354	$67.04	$67.05	$67.00
Purchase #7	$55.29	3.362%	$57.1488	$57.15	$57.15	$57.10
7 purchase totals =	$744.70		$809.2199	$809.22	$809.20	$809.20