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	$45.71	10.174%	$50.3605	$50.36	$50.35	$50.40
Purchase #2	$243.80	8.686%	$264.9765	$264.98	$265.00	$265.00
Purchase #3	$30.77	5.371%	$32.4227	$32.42	$32.40	$32.40
Purchase #4	$83.77	7.256%	$89.8484	$89.85	$89.85	$89.80
Purchase #5	$56.89	11.291%	$63.3134	$63.31	$63.30	$63.30
Purchase #6	$197.46	12.474%	$222.0912	$222.09	$222.10	$222.10
Purchase #7	$235.99	4.759%	$247.2208	$247.22	$247.20	$247.20
7 purchase totals =	$894.39		$970.2335	$970.23	$970.20	$970.20