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	$49.55	6.236%	$52.6399	$52.64	$52.65	$52.60
Purchase #2	$99.90	12.229%	$112.1168	$112.12	$112.10	$112.10
Purchase #3	$84.63	8.610%	$91.9166	$91.92	$91.90	$91.90
Purchase #4	$247.78	4.747%	$259.5421	$259.54	$259.55	$259.50
Purchase #5	$106.53	9.734%	$116.8996	$116.90	$116.90	$116.90
Purchase #6	$15.39	3.299%	$15.8977	$15.90	$15.90	$15.90
Purchase #7	$212.83	3.281%	$219.813	$219.81	$219.80	$219.80
7 purchase totals =	$816.61		$868.8257	$868.83	$868.80	$868.70