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	$122.53	7.637%	$131.8876	$131.89	$131.90	$131.90
Purchase #2	$211.39	5.384%	$222.7712	$222.77	$222.75	$222.80
Purchase #3	$167.51	7.634%	$180.2977	$180.30	$180.30	$180.30
Purchase #4	$45.25	9.240%	$49.4311	$49.43	$49.45	$49.40
Purchase #5	$76.91	12.871%	$86.8091	$86.81	$86.80	$86.80
Purchase #6	$165.66	4.158%	$172.5481	$172.55	$172.55	$172.50
Purchase #7	$70.87	3.114%	$73.0769	$73.08	$73.10	$73.10
7 purchase totals =	$860.12		$916.8217	$916.83	$916.85	$916.80