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	$67.72	7.534%	$72.822	$72.82	$72.80	$72.80
Purchase #2	$229.52	12.660%	$258.5772	$258.58	$258.60	$258.60
Purchase #3	$157.25	6.429%	$167.3596	$167.36	$167.35	$167.40
Purchase #4	$161.89	4.303%	$168.8561	$168.86	$168.85	$168.90
Purchase #5	$225.40	9.642%	$247.1331	$247.13	$247.15	$247.10
Purchase #6	$144.27	10.477%	$159.3852	$159.39	$159.40	$159.40
Purchase #7	$50.58	13.161%	$57.2368	$57.24	$57.25	$57.20
7 purchase totals =	$1,036.63		$1,131.3700	$1,131.38	$1,131.40	$1,131.40