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	$10.47	6.600%	$11.161	$11.16	$11.15	$11.20
Purchase #2	$223.75	4.785%	$234.4564	$234.46	$234.45	$234.50
Purchase #3	$32.51	4.220%	$33.8819	$33.88	$33.90	$33.90
Purchase #4	$87.27	12.778%	$98.4214	$98.42	$98.40	$98.40
Purchase #5	$30.59	13.129%	$34.6062	$34.61	$34.60	$34.60
Purchase #6	$167.34	4.453%	$174.7917	$174.79	$174.80	$174.80
Purchase #7	$57.34	9.104%	$62.5602	$62.56	$62.55	$62.60
7 purchase totals =	$609.27		$649.8788	$649.88	$649.85	$650.00