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	$29.57	11.851%	$33.0743	$33.07	$33.05	$33.10
Purchase #2	$83.57	10.518%	$92.3599	$92.36	$92.35	$92.40
Purchase #3	$122.85	11.174%	$136.5773	$136.58	$136.60	$136.60
Purchase #4	$94.63	11.695%	$105.697	$105.70	$105.70	$105.70
Purchase #5	$64.26	4.646%	$67.2455	$67.25	$67.25	$67.20
Purchase #6	$153.64	5.847%	$162.6233	$162.62	$162.60	$162.60
Purchase #7	$50.78	3.616%	$52.6162	$52.62	$52.60	$52.60
7 purchase totals =	$599.30		$650.1935	$650.20	$650.15	$650.20