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	$105.46	12.251%	$118.3799	$118.38	$118.40	$118.40
Purchase #2	$180.99	5.810%	$191.5055	$191.51	$191.50	$191.50
Purchase #3	$176.78	4.234%	$184.2649	$184.26	$184.25	$184.30
Purchase #4	$221.73	7.250%	$237.8054	$237.81	$237.80	$237.80
Purchase #5	$176.25	10.586%	$194.9078	$194.91	$194.90	$194.90
Purchase #6	$136.80	10.650%	$151.3692	$151.37	$151.35	$151.40
Purchase #7	$225.87	12.848%	$254.8898	$254.89	$254.90	$254.90
7 purchase totals =	$1,223.88		$1,333.1225	$1,333.13	$1,333.10	$1,333.20