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	$92.50	12.729%	$104.2743	$104.27	$104.25	$104.30
Purchase #2	$55.33	12.330%	$62.1522	$62.15	$62.15	$62.20
Purchase #3	$78.79	8.871%	$85.7795	$85.78	$85.80	$85.80
Purchase #4	$157.64	5.178%	$165.8026	$165.80	$165.80	$165.80
Purchase #5	$135.54	3.187%	$139.8597	$139.86	$139.85	$139.90
Purchase #6	$148.31	3.571%	$153.6062	$153.61	$153.60	$153.60
Purchase #7	$99.97	7.102%	$107.0699	$107.07	$107.05	$107.10
7 purchase totals =	$768.08		$818.5444	$818.54	$818.50	$818.70