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	$9.90	13.600%	$11.2464	$11.25	$11.25	$11.20
Purchase #2	$220.63	6.138%	$234.1723	$234.17	$234.15	$234.20
Purchase #3	$143.47	8.793%	$156.0853	$156.09	$156.10	$156.10
Purchase #4	$205.78	13.500%	$233.5603	$233.56	$233.55	$233.60
Purchase #5	$244.43	7.559%	$262.9065	$262.91	$262.90	$262.90
Purchase #6	$223.51	13.870%	$254.5108	$254.51	$254.50	$254.50
Purchase #7	$248.90	11.448%	$277.3941	$277.39	$277.40	$277.40
7 purchase totals =	$1,296.62		$1,429.8757	$1,429.88	$1,429.85	$1,429.90