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	$136.35	9.329%	$149.0701	$149.07	$149.05	$149.10
Purchase #2	$45.53	13.588%	$51.7166	$51.72	$51.70	$51.70
Purchase #3	$20.75	5.103%	$21.8089	$21.81	$21.80	$21.80
Purchase #4	$100.62	4.661%	$105.3099	$105.31	$105.30	$105.30
Purchase #5	$129.98	5.613%	$137.2758	$137.28	$137.30	$137.30
Purchase #6	$6.97	8.259%	$7.5457	$7.55	$7.55	$7.50
Purchase #7	$24.37	4.801%	$25.54	$25.54	$25.55	$25.50
7 purchase totals =	$464.57		$498.2670	$498.28	$498.25	$498.20