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	$14.64	4.309%	$15.2708	$15.27	$15.25	$15.30
Purchase #2	$137.56	6.200%	$146.0887	$146.09	$146.10	$146.10
Purchase #3	$33.54	11.399%	$37.3632	$37.36	$37.35	$37.40
Purchase #4	$45.43	9.471%	$49.7327	$49.73	$49.75	$49.70
Purchase #5	$107.66	6.376%	$114.5244	$114.52	$114.50	$114.50
Purchase #6	$31.73	8.172%	$34.323	$34.32	$34.30	$34.30
Purchase #7	$56.72	12.800%	$63.9802	$63.98	$64.00	$64.00
7 purchase totals =	$427.28		$461.2830	$461.27	$461.25	$461.30