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	$237.72	11.309%	$264.6038	$264.60	$264.60	$264.60
Purchase #2	$114.95	7.445%	$123.508	$123.51	$123.50	$123.50
Purchase #3	$54.64	6.191%	$58.0228	$58.02	$58.00	$58.00
Purchase #4	$37.70	13.286%	$42.7088	$42.71	$42.70	$42.70
Purchase #5	$62.25	8.502%	$67.5425	$67.54	$67.55	$67.50
Purchase #6	$235.62	5.418%	$248.3859	$248.39	$248.40	$248.40
Purchase #7	$79.37	5.393%	$83.6504	$83.65	$83.65	$83.70
7 purchase totals =	$822.25		$888.4222	$888.42	$888.40	$888.40