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	$243.92	13.373%	$276.5394	$276.54	$276.55	$276.50
Purchase #2	$152.82	12.873%	$172.4925	$172.49	$172.50	$172.50
Purchase #3	$95.37	5.131%	$100.2634	$100.26	$100.25	$100.30
Purchase #4	$221.49	9.521%	$242.5781	$242.58	$242.60	$242.60
Purchase #5	$32.61	4.166%	$33.9685	$33.97	$33.95	$34.00
Purchase #6	$236.87	13.468%	$268.7717	$268.77	$268.75	$268.80
Purchase #7	$92.49	4.702%	$96.8389	$96.84	$96.85	$96.80
7 purchase totals =	$1,075.57		$1,191.4525	$1,191.45	$1,191.45	$1,191.50