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	$239.59	11.186%	$266.3905	$266.39	$266.40	$266.40
Purchase #2	$175.60	5.500%	$185.258	$185.26	$185.25	$185.30
Purchase #3	$250.63	9.690%	$274.916	$274.92	$274.90	$274.90
Purchase #4	$153.98	12.131%	$172.6593	$172.66	$172.65	$172.70
Purchase #5	$29.62	6.779%	$31.6279	$31.63	$31.65	$31.60
Purchase #6	$131.73	6.526%	$140.3267	$140.33	$140.35	$140.30
Purchase #7	$143.57	7.322%	$154.0822	$154.08	$154.10	$154.10
7 purchase totals =	$1,124.72		$1,225.2606	$1,225.27	$1,225.30	$1,225.30