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	$106.61	5.201%	$112.1548	$112.15	$112.15	$112.20
Purchase #2	$145.49	10.183%	$160.3052	$160.31	$160.30	$160.30
Purchase #3	$139.56	13.690%	$158.6658	$158.67	$158.65	$158.70
Purchase #4	$198.87	8.826%	$216.4223	$216.42	$216.40	$216.40
Purchase #5	$45.51	12.800%	$51.3353	$51.34	$51.35	$51.30
Purchase #6	$29.41	13.411%	$33.3542	$33.35	$33.35	$33.40
Purchase #7	$140.98	12.494%	$158.594	$158.59	$158.60	$158.60
7 purchase totals =	$806.43		$890.8316	$890.83	$890.80	$890.90