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	$72.50	3.717%	$75.1948	$75.19	$75.20	$75.20
Purchase #2	$99.82	4.676%	$104.4876	$104.49	$104.50	$104.50
Purchase #3	$87.63	13.300%	$99.2848	$99.28	$99.30	$99.30
Purchase #4	$48.92	8.808%	$53.2289	$53.23	$53.25	$53.20
Purchase #5	$170.79	8.724%	$185.6897	$185.69	$185.70	$185.70
Purchase #6	$63.76	13.479%	$72.3542	$72.35	$72.35	$72.40
Purchase #7	$11.67	10.119%	$12.8509	$12.85	$12.85	$12.90
7 purchase totals =	$555.09		$603.0909	$603.08	$603.15	$603.20