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	$55.91	6.287%	$59.4251	$59.43	$59.45	$59.40
Purchase #2	$17.51	12.318%	$19.6669	$19.67	$19.65	$19.70
Purchase #3	$42.68	9.400%	$46.6919	$46.69	$46.70	$46.70
Purchase #4	$19.84	11.846%	$22.1902	$22.19	$22.20	$22.20
Purchase #5	$48.93	10.139%	$53.891	$53.89	$53.90	$53.90
Purchase #6	$168.74	10.478%	$186.4206	$186.42	$186.40	$186.40
Purchase #7	$101.69	9.721%	$111.5753	$111.58	$111.60	$111.60
7 purchase totals =	$455.30		$499.8610	$499.87	$499.90	$499.90