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	$236.77	9.476%	$259.2063	$259.21	$259.20	$259.20
Purchase #2	$219.40	8.705%	$238.4988	$238.50	$238.50	$238.50
Purchase #3	$33.49	13.139%	$37.8903	$37.89	$37.90	$37.90
Purchase #4	$51.45	8.209%	$55.6735	$55.67	$55.65	$55.70
Purchase #5	$167.79	7.146%	$179.7803	$179.78	$179.80	$179.80
Purchase #6	$106.35	10.683%	$117.7114	$117.71	$117.70	$117.70
Purchase #7	$103.41	4.712%	$108.2827	$108.28	$108.30	$108.30
7 purchase totals =	$918.66		$997.0433	$997.04	$997.05	$997.10