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	$175.42	8.257%	$189.9044	$189.90	$189.90	$189.90
Purchase #2	$229.96	13.579%	$261.1863	$261.19	$261.20	$261.20
Purchase #3	$223.90	3.152%	$230.9573	$230.96	$230.95	$231.00
Purchase #4	$110.59	7.120%	$118.464	$118.46	$118.45	$118.50
Purchase #5	$62.29	6.262%	$66.1906	$66.19	$66.20	$66.20
Purchase #6	$233.97	9.532%	$256.272	$256.27	$256.25	$256.30
Purchase #7	$87.68	13.286%	$99.3292	$99.33	$99.35	$99.30
7 purchase totals =	$1,123.81		$1,222.3038	$1,222.30	$1,222.30	$1,222.40