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	$51.33	5.497%	$54.1516	$54.15	$54.15	$54.20
Purchase #2	$156.43	5.614%	$165.212	$165.21	$165.20	$165.20
Purchase #3	$39.37	11.132%	$43.7527	$43.75	$43.75	$43.80
Purchase #4	$124.89	9.788%	$137.1142	$137.11	$137.10	$137.10
Purchase #5	$81.70	5.181%	$85.9329	$85.93	$85.95	$85.90
Purchase #6	$11.47	6.205%	$12.1817	$12.18	$12.20	$12.20
Purchase #7	$78.61	8.854%	$85.5701	$85.57	$85.55	$85.60
7 purchase totals =	$543.80		$583.9152	$583.90	$583.90	$584.00