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	$237.74	5.394%	$250.5637	$250.56	$250.55	$250.60
Purchase #2	$48.65	10.383%	$53.7013	$53.70	$53.70	$53.70
Purchase #3	$30.88	9.466%	$33.8031	$33.80	$33.80	$33.80
Purchase #4	$46.89	3.111%	$48.3487	$48.35	$48.35	$48.30
Purchase #5	$82.29	3.754%	$85.3792	$85.38	$85.40	$85.40
Purchase #6	$44.87	11.707%	$50.1229	$50.12	$50.10	$50.10
Purchase #7	$65.65	4.372%	$68.5202	$68.52	$68.50	$68.50
7 purchase totals =	$556.97		$590.4391	$590.43	$590.40	$590.40