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	$9.81	3.717%	$10.1746	$10.17	$10.15	$10.20
Purchase #2	$136.81	3.580%	$141.7078	$141.71	$141.70	$141.70
Purchase #3	$128.27	8.400%	$139.0447	$139.04	$139.05	$139.00
Purchase #4	$152.90	9.267%	$167.0692	$167.07	$167.05	$167.10
Purchase #5	$46.32	10.259%	$51.072	$51.07	$51.05	$51.10
Purchase #6	$49.63	10.500%	$54.8412	$54.84	$54.85	$54.80
Purchase #7	$92.74	9.419%	$101.4752	$101.48	$101.50	$101.50
7 purchase totals =	$616.48		$665.3847	$665.38	$665.35	$665.40