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	$85.52	12.573%	$96.2724	$96.27	$96.25	$96.30
Purchase #2	$13.39	6.403%	$14.2474	$14.25	$14.25	$14.20
Purchase #3	$120.46	8.521%	$130.7244	$130.72	$130.70	$130.70
Purchase #4	$15.31	12.185%	$17.1755	$17.18	$17.20	$17.20
Purchase #5	$100.91	12.685%	$113.7104	$113.71	$113.70	$113.70
Purchase #6	$106.89	11.264%	$118.9301	$118.93	$118.95	$118.90
Purchase #7	$64.34	11.636%	$71.8266	$71.83	$71.85	$71.80
7 purchase totals =	$506.82		$562.8868	$562.89	$562.90	$562.80