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	$139.49	3.727%	$144.6888	$144.69	$144.70	$144.70
Purchase #2	$244.83	13.454%	$277.7694	$277.77	$277.75	$277.80
Purchase #3	$162.72	6.501%	$173.2984	$173.30	$173.30	$173.30
Purchase #4	$109.96	12.117%	$123.2839	$123.28	$123.30	$123.30
Purchase #5	$75.37	7.573%	$81.0778	$81.08	$81.10	$81.10
Purchase #6	$86.29	3.707%	$89.4888	$89.49	$89.50	$89.50
Purchase #7	$75.89	3.160%	$78.2881	$78.29	$78.30	$78.30
7 purchase totals =	$894.55		$967.8952	$967.90	$967.95	$968.00