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	$47.80	13.245%	$54.1311	$54.13	$54.15	$54.10
Purchase #2	$247.98	4.592%	$259.3672	$259.37	$259.35	$259.40
Purchase #3	$247.72	11.229%	$275.5365	$275.54	$275.55	$275.50
Purchase #4	$145.77	9.512%	$159.6356	$159.64	$159.65	$159.60
Purchase #5	$85.51	10.428%	$94.427	$94.43	$94.45	$94.40
Purchase #6	$132.72	8.501%	$144.0025	$144.00	$144.00	$144.00
Purchase #7	$236.40	13.473%	$268.2502	$268.25	$268.25	$268.30
7 purchase totals =	$1,143.90		$1,255.3501	$1,255.36	$1,255.40	$1,255.30