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	$234.95	6.798%	$250.9219	$250.92	$250.90	$250.90
Purchase #2	$106.57	3.738%	$110.5536	$110.55	$110.55	$110.60
Purchase #3	$220.43	4.586%	$230.5389	$230.54	$230.55	$230.50
Purchase #4	$185.37	13.323%	$210.0668	$210.07	$210.05	$210.10
Purchase #5	$164.56	7.284%	$176.5466	$176.55	$176.55	$176.50
Purchase #6	$12.67	11.316%	$14.1037	$14.10	$14.10	$14.10
Purchase #7	$158.90	13.140%	$179.7795	$179.78	$179.80	$179.80
7 purchase totals =	$1,083.45		$1,172.5110	$1,172.51	$1,172.50	$1,172.50