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	$73.39	5.531%	$77.4492	$77.45	$77.45	$77.40
Purchase #2	$90.83	10.503%	$100.3699	$100.37	$100.35	$100.40
Purchase #3	$81.39	12.369%	$91.4571	$91.46	$91.45	$91.50
Purchase #4	$161.87	10.392%	$178.6915	$178.69	$178.70	$178.70
Purchase #5	$126.28	11.718%	$141.0775	$141.08	$141.10	$141.10
Purchase #6	$99.25	5.104%	$104.3157	$104.32	$104.30	$104.30
Purchase #7	$157.59	8.696%	$171.294	$171.29	$171.30	$171.30
7 purchase totals =	$790.60		$864.6549	$864.66	$864.65	$864.70