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	$233.81	9.689%	$256.4639	$256.46	$256.45	$256.50
Purchase #2	$250.25	3.832%	$259.8396	$259.84	$259.85	$259.80
Purchase #3	$96.75	7.336%	$103.8476	$103.85	$103.85	$103.80
Purchase #4	$152.52	3.640%	$158.0717	$158.07	$158.05	$158.10
Purchase #5	$108.36	10.640%	$119.8895	$119.89	$119.90	$119.90
Purchase #6	$17.27	6.777%	$18.4404	$18.44	$18.45	$18.40
Purchase #7	$151.52	11.348%	$168.7145	$168.71	$168.70	$168.70
7 purchase totals =	$1,010.48		$1,085.2672	$1,085.26	$1,085.25	$1,085.20