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	$79.88	10.530%	$88.2914	$88.29	$88.30	$88.30
Purchase #2	$98.37	13.651%	$111.7985	$111.80	$111.80	$111.80
Purchase #3	$176.32	7.333%	$189.2495	$189.25	$189.25	$189.20
Purchase #4	$190.82	12.376%	$214.4359	$214.44	$214.45	$214.40
Purchase #5	$42.96	3.260%	$44.3605	$44.36	$44.35	$44.40
Purchase #6	$135.65	3.128%	$139.8931	$139.89	$139.90	$139.90
Purchase #7	$80.50	11.316%	$89.6094	$89.61	$89.60	$89.60
7 purchase totals =	$804.50		$877.6383	$877.64	$877.65	$877.60