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	$32.75	13.497%	$37.1703	$37.17	$37.15	$37.20
Purchase #2	$228.31	3.762%	$236.899	$236.90	$236.90	$236.90
Purchase #3	$203.74	11.463%	$227.0947	$227.09	$227.10	$227.10
Purchase #4	$75.90	3.861%	$78.8305	$78.83	$78.85	$78.80
Purchase #5	$16.68	10.249%	$18.3895	$18.39	$18.40	$18.40
Purchase #6	$246.72	11.604%	$275.3494	$275.35	$275.35	$275.30
Purchase #7	$41.97	7.424%	$45.0859	$45.09	$45.10	$45.10
7 purchase totals =	$846.07		$918.8193	$918.82	$918.85	$918.80