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	$26.42	11.625%	$29.4913	$29.49	$29.50	$29.50
Purchase #2	$203.38	8.774%	$221.2246	$221.22	$221.20	$221.20
Purchase #3	$80.66	13.418%	$91.483	$91.48	$91.50	$91.50
Purchase #4	$127.92	5.411%	$134.8418	$134.84	$134.85	$134.80
Purchase #5	$50.95	10.765%	$56.4348	$56.43	$56.45	$56.40
Purchase #6	$153.78	12.403%	$172.8533	$172.85	$172.85	$172.90
Purchase #7	$32.39	3.760%	$33.6079	$33.61	$33.60	$33.60
7 purchase totals =	$675.50		$739.9367	$739.92	$739.95	$739.90