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	$157.83	9.555%	$172.9107	$172.91	$172.90	$172.90
Purchase #2	$141.70	11.844%	$158.4829	$158.48	$158.50	$158.50
Purchase #3	$217.66	7.290%	$233.5274	$233.53	$233.55	$233.50
Purchase #4	$235.71	13.844%	$268.3417	$268.34	$268.35	$268.30
Purchase #5	$205.27	8.584%	$222.8904	$222.89	$222.90	$222.90
Purchase #6	$5.83	5.622%	$6.1578	$6.16	$6.15	$6.20
Purchase #7	$218.94	4.437%	$228.6544	$228.65	$228.65	$228.70
7 purchase totals =	$1,182.94		$1,290.9653	$1,290.96	$1,291.00	$1,291.00