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	$138.30	8.658%	$150.274	$150.27	$150.25	$150.30
Purchase #2	$243.42	4.273%	$253.8213	$253.82	$253.80	$253.80
Purchase #3	$118.65	5.426%	$125.0879	$125.09	$125.10	$125.10
Purchase #4	$234.73	9.442%	$256.8932	$256.89	$256.90	$256.90
Purchase #5	$210.97	10.658%	$233.4552	$233.46	$233.45	$233.50
Purchase #6	$11.64	10.597%	$12.8735	$12.87	$12.85	$12.90
Purchase #7	$190.53	13.274%	$215.821	$215.82	$215.80	$215.80
7 purchase totals =	$1,148.24		$1,248.2261	$1,248.22	$1,248.15	$1,248.30