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	$19.48	3.363%	$20.1351	$20.14	$20.15	$20.10
Purchase #2	$55.81	5.616%	$58.9443	$58.94	$58.95	$58.90
Purchase #3	$18.35	10.664%	$20.3068	$20.31	$20.30	$20.30
Purchase #4	$207.83	13.549%	$235.9889	$235.99	$236.00	$236.00
Purchase #5	$73.78	11.206%	$82.0478	$82.05	$82.05	$82.00
Purchase #6	$40.89	3.821%	$42.4524	$42.45	$42.45	$42.50
Purchase #7	$91.32	9.622%	$100.1068	$100.11	$100.10	$100.10
7 purchase totals =	$507.46		$559.9821	$559.99	$560.00	$559.90