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	$238.82	4.800%	$250.2834	$250.28	$250.30	$250.30
Purchase #2	$207.78	7.515%	$223.3947	$223.39	$223.40	$223.40
Purchase #3	$105.97	7.831%	$114.2685	$114.27	$114.25	$114.30
Purchase #4	$45.95	7.615%	$49.4491	$49.45	$49.45	$49.40
Purchase #5	$37.52	6.446%	$39.9385	$39.94	$39.95	$39.90
Purchase #6	$53.48	5.797%	$56.5802	$56.58	$56.60	$56.60
Purchase #7	$59.49	13.198%	$67.3415	$67.34	$67.35	$67.30
7 purchase totals =	$749.01		$801.2559	$801.25	$801.30	$801.20