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	$11.40	12.746%	$12.853	$12.85	$12.85	$12.90
Purchase #2	$96.57	8.139%	$104.4298	$104.43	$104.45	$104.40
Purchase #3	$224.43	12.399%	$252.2571	$252.26	$252.25	$252.30
Purchase #4	$43.81	4.823%	$45.923	$45.92	$45.90	$45.90
Purchase #5	$188.91	8.519%	$205.0032	$205.00	$205.00	$205.00
Purchase #6	$54.81	8.794%	$59.63	$59.63	$59.65	$59.60
Purchase #7	$11.85	12.841%	$13.3717	$13.37	$13.35	$13.40
7 purchase totals =	$631.78		$693.4678	$693.46	$693.45	$693.50