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	$149.83	10.446%	$165.4812	$165.48	$165.50	$165.50
Purchase #2	$54.37	9.805%	$59.701	$59.70	$59.70	$59.70
Purchase #3	$77.89	8.132%	$84.224	$84.22	$84.20	$84.20
Purchase #4	$37.71	9.371%	$41.2438	$41.24	$41.25	$41.20
Purchase #5	$168.42	7.159%	$180.4772	$180.48	$180.50	$180.50
Purchase #6	$49.47	5.663%	$52.2715	$52.27	$52.25	$52.30
Purchase #7	$53.32	3.481%	$55.1761	$55.18	$55.20	$55.20
7 purchase totals =	$591.01		$638.5748	$638.57	$638.60	$638.60