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	$227.71	13.524%	$258.5055	$258.51	$258.50	$258.50
Purchase #2	$199.31	9.219%	$217.6844	$217.68	$217.70	$217.70
Purchase #3	$34.47	7.679%	$37.117	$37.12	$37.10	$37.10
Purchase #4	$234.64	10.783%	$259.9412	$259.94	$259.95	$259.90
Purchase #5	$196.62	12.305%	$220.8141	$220.81	$220.80	$220.80
Purchase #6	$28.32	11.456%	$31.5643	$31.56	$31.55	$31.60
Purchase #7	$148.64	11.373%	$165.5448	$165.54	$165.55	$165.50
7 purchase totals =	$1,069.71		$1,191.1713	$1,191.16	$1,191.15	$1,191.10