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	$167.86	13.647%	$190.7679	$190.77	$190.75	$190.80
Purchase #2	$188.30	3.753%	$195.3669	$195.37	$195.35	$195.40
Purchase #3	$196.32	7.708%	$211.4523	$211.45	$211.45	$211.50
Purchase #4	$88.71	12.106%	$99.4492	$99.45	$99.45	$99.40
Purchase #5	$85.32	13.208%	$96.5891	$96.59	$96.60	$96.60
Purchase #6	$137.95	5.849%	$146.0187	$146.02	$146.00	$146.00
Purchase #7	$51.96	8.277%	$56.2607	$56.26	$56.25	$56.30
7 purchase totals =	$916.42		$995.9048	$995.91	$995.85	$996.00