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	$179.33	4.424%	$187.2636	$187.26	$187.25	$187.30
Purchase #2	$61.86	9.135%	$67.5109	$67.51	$67.50	$67.50
Purchase #3	$58.75	6.574%	$62.6122	$62.61	$62.60	$62.60
Purchase #4	$17.74	13.475%	$20.1305	$20.13	$20.15	$20.10
Purchase #5	$73.67	6.687%	$78.5963	$78.60	$78.60	$78.60
Purchase #6	$74.31	7.388%	$79.8	$79.80	$79.80	$79.80
Purchase #7	$123.80	11.829%	$138.4443	$138.44	$138.45	$138.40
7 purchase totals =	$589.46		$634.3578	$634.35	$634.35	$634.30