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	$230.78	11.265%	$256.7774	$256.78	$256.80	$256.80
Purchase #2	$248.98	12.251%	$279.4825	$279.48	$279.50	$279.50
Purchase #3	$22.37	13.764%	$25.449	$25.45	$25.45	$25.40
Purchase #4	$20.32	3.144%	$20.9589	$20.96	$20.95	$21.00
Purchase #5	$79.38	8.214%	$85.9003	$85.90	$85.90	$85.90
Purchase #6	$137.76	4.775%	$144.338	$144.34	$144.35	$144.30
Purchase #7	$12.95	3.345%	$13.3832	$13.38	$13.40	$13.40
7 purchase totals =	$752.54		$826.2893	$826.29	$826.35	$826.30