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	$232.45	4.739%	$243.4658	$243.47	$243.45	$243.50
Purchase #2	$24.61	11.820%	$27.5189	$27.52	$27.50	$27.50
Purchase #3	$170.37	4.379%	$177.8305	$177.83	$177.85	$177.80
Purchase #4	$131.85	12.307%	$148.0768	$148.08	$148.10	$148.10
Purchase #5	$7.78	4.611%	$8.1387	$8.14	$8.15	$8.10
Purchase #6	$12.29	8.527%	$13.338	$13.34	$13.35	$13.30
Purchase #7	$67.50	5.459%	$71.1848	$71.18	$71.20	$71.20
7 purchase totals =	$646.85		$689.5535	$689.56	$689.60	$689.50