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	$205.37	7.648%	$221.0767	$221.08	$221.10	$221.10
Purchase #2	$250.41	6.314%	$266.2209	$266.22	$266.20	$266.20
Purchase #3	$59.92	4.821%	$62.8087	$62.81	$62.80	$62.80
Purchase #4	$86.29	5.262%	$90.8306	$90.83	$90.85	$90.80
Purchase #5	$86.50	5.845%	$91.5559	$91.56	$91.55	$91.60
Purchase #6	$188.55	10.223%	$207.8255	$207.83	$207.85	$207.80
Purchase #7	$50.78	6.552%	$54.1071	$54.11	$54.10	$54.10
7 purchase totals =	$927.82		$994.4254	$994.44	$994.45	$994.40