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	$46.78	13.612%	$53.1477	$53.15	$53.15	$53.10
Purchase #2	$105.63	11.650%	$117.9359	$117.94	$117.95	$117.90
Purchase #3	$171.46	4.593%	$179.3352	$179.34	$179.35	$179.30
Purchase #4	$114.50	4.610%	$119.7785	$119.78	$119.80	$119.80
Purchase #5	$12.65	13.309%	$14.3336	$14.33	$14.35	$14.30
Purchase #6	$9.41	13.150%	$10.6474	$10.65	$10.65	$10.60
Purchase #7	$52.61	8.837%	$57.2591	$57.26	$57.25	$57.30
7 purchase totals =	$513.04		$552.4374	$552.45	$552.50	$552.30