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	$34.56	7.436%	$37.1299	$37.13	$37.15	$37.10
Purchase #2	$35.63	6.333%	$37.8864	$37.89	$37.90	$37.90
Purchase #3	$72.29	13.362%	$81.9494	$81.95	$81.95	$81.90
Purchase #4	$127.74	8.478%	$138.5698	$138.57	$138.55	$138.60
Purchase #5	$74.85	4.623%	$78.3103	$78.31	$78.30	$78.30
Purchase #6	$153.82	12.618%	$173.229	$173.23	$173.25	$173.20
Purchase #7	$157.31	5.279%	$165.6144	$165.61	$165.60	$165.60
7 purchase totals =	$656.20		$712.6892	$712.69	$712.70	$712.60