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	$30.79	12.104%	$34.5168	$34.52	$34.50	$34.50
Purchase #2	$205.62	8.691%	$223.4904	$223.49	$223.50	$223.50
Purchase #3	$66.70	3.803%	$69.2366	$69.24	$69.25	$69.20
Purchase #4	$152.94	8.195%	$165.4734	$165.47	$165.45	$165.50
Purchase #5	$90.71	11.263%	$100.9267	$100.93	$100.95	$100.90
Purchase #6	$156.54	5.560%	$165.2436	$165.24	$165.25	$165.20
Purchase #7	$57.27	11.650%	$63.942	$63.94	$63.95	$63.90
7 purchase totals =	$760.57		$822.8295	$822.83	$822.85	$822.70