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	$122.52	6.294%	$130.2314	$130.23	$130.25	$130.20
Purchase #2	$61.47	9.508%	$67.3146	$67.31	$67.30	$67.30
Purchase #3	$220.59	11.726%	$246.4564	$246.46	$246.45	$246.50
Purchase #4	$212.87	12.667%	$239.8342	$239.83	$239.85	$239.80
Purchase #5	$105.56	11.550%	$117.7522	$117.75	$117.75	$117.80
Purchase #6	$151.91	13.843%	$172.9389	$172.94	$172.95	$172.90
Purchase #7	$31.48	12.146%	$35.3036	$35.30	$35.30	$35.30
7 purchase totals =	$906.40		$1,009.8313	$1,009.82	$1,009.85	$1,009.80