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	$135.81	6.461%	$144.5847	$144.58	$144.60	$144.60
Purchase #2	$152.76	12.428%	$171.745	$171.75	$171.75	$171.70
Purchase #3	$225.86	13.750%	$256.9158	$256.92	$256.90	$256.90
Purchase #4	$61.90	8.518%	$67.1726	$67.17	$67.15	$67.20
Purchase #5	$77.83	3.120%	$80.2583	$80.26	$80.25	$80.30
Purchase #6	$125.43	13.635%	$142.5324	$142.53	$142.55	$142.50
Purchase #7	$99.41	11.301%	$110.6443	$110.64	$110.65	$110.60
7 purchase totals =	$879.00		$973.8531	$973.85	$973.85	$973.80