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	$242.79	13.271%	$275.0107	$275.01	$275.00	$275.00
Purchase #2	$7.32	5.328%	$7.71	$7.71	$7.70	$7.70
Purchase #3	$57.69	6.847%	$61.64	$61.64	$61.65	$61.60
Purchase #4	$217.35	5.294%	$228.8565	$228.86	$228.85	$228.90
Purchase #5	$89.82	11.603%	$100.2418	$100.24	$100.25	$100.20
Purchase #6	$134.49	9.420%	$147.159	$147.16	$147.15	$147.20
Purchase #7	$33.66	10.499%	$37.194	$37.19	$37.20	$37.20
7 purchase totals =	$783.12		$857.8120	$857.81	$857.80	$857.80