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	$26.85	13.707%	$30.5303	$30.53	$30.55	$30.50
Purchase #2	$235.93	12.673%	$265.8294	$265.83	$265.85	$265.80
Purchase #3	$132.82	8.738%	$144.4258	$144.43	$144.45	$144.40
Purchase #4	$248.89	4.770%	$260.7621	$260.76	$260.75	$260.80
Purchase #5	$236.41	5.808%	$250.1407	$250.14	$250.15	$250.10
Purchase #6	$114.63	11.568%	$127.8904	$127.89	$127.90	$127.90
Purchase #7	$28.78	10.488%	$31.7984	$31.80	$31.80	$31.80
7 purchase totals =	$1,024.31		$1,111.3771	$1,111.38	$1,111.45	$1,111.30