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	$42.86	5.694%	$45.3004	$45.30	$45.30	$45.30
Purchase #2	$196.93	12.395%	$221.3395	$221.34	$221.35	$221.30
Purchase #3	$128.34	6.783%	$137.0453	$137.05	$137.05	$137.00
Purchase #4	$11.32	6.562%	$12.0628	$12.06	$12.05	$12.10
Purchase #5	$37.73	5.429%	$39.7784	$39.78	$39.80	$39.80
Purchase #6	$57.71	13.829%	$65.6907	$65.69	$65.70	$65.70
Purchase #7	$113.66	13.328%	$128.8086	$128.81	$128.80	$128.80
7 purchase totals =	$588.55		$650.0257	$650.03	$650.05	$650.00