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	$22.33	9.146%	$24.3723	$24.37	$24.35	$24.40
Purchase #2	$72.41	8.210%	$78.3549	$78.35	$78.35	$78.40
Purchase #3	$219.46	6.423%	$233.5559	$233.56	$233.55	$233.60
Purchase #4	$102.50	8.315%	$111.0229	$111.02	$111.00	$111.00
Purchase #5	$140.78	13.422%	$159.6755	$159.68	$159.70	$159.70
Purchase #6	$105.93	9.720%	$116.2264	$116.23	$116.25	$116.20
Purchase #7	$205.33	7.777%	$221.2985	$221.30	$221.30	$221.30
7 purchase totals =	$868.74		$944.5064	$944.51	$944.50	$944.60