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	$250.92	9.742%	$275.3646	$275.36	$275.35	$275.40
Purchase #2	$248.34	4.613%	$259.7959	$259.80	$259.80	$259.80
Purchase #3	$19.88	13.582%	$22.5801	$22.58	$22.60	$22.60
Purchase #4	$95.74	9.271%	$104.6161	$104.62	$104.60	$104.60
Purchase #5	$68.88	5.223%	$72.4776	$72.48	$72.50	$72.50
Purchase #6	$198.47	12.499%	$223.2768	$223.28	$223.30	$223.30
Purchase #7	$228.92	5.851%	$242.3141	$242.31	$242.30	$242.30
7 purchase totals =	$1,111.15		$1,200.4252	$1,200.43	$1,200.45	$1,200.50