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	$19.59	10.560%	$21.6587	$21.66	$21.65	$21.70
Purchase #2	$183.54	11.651%	$204.9242	$204.92	$204.90	$204.90
Purchase #3	$37.62	7.334%	$40.3791	$40.38	$40.40	$40.40
Purchase #4	$141.54	12.140%	$158.723	$158.72	$158.70	$158.70
Purchase #5	$32.91	9.487%	$36.0322	$36.03	$36.05	$36.00
Purchase #6	$39.86	13.867%	$45.3874	$45.39	$45.40	$45.40
Purchase #7	$159.54	7.698%	$171.8214	$171.82	$171.80	$171.80
7 purchase totals =	$614.60		$678.9260	$678.92	$678.90	$678.90