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	$79.94	9.318%	$87.3888	$87.39	$87.40	$87.40
Purchase #2	$55.39	9.241%	$60.5086	$60.51	$60.50	$60.50
Purchase #3	$98.39	13.410%	$111.5841	$111.58	$111.60	$111.60
Purchase #4	$52.51	12.540%	$59.0948	$59.09	$59.10	$59.10
Purchase #5	$129.57	11.632%	$144.6416	$144.64	$144.65	$144.60
Purchase #6	$56.80	6.179%	$60.3097	$60.31	$60.30	$60.30
Purchase #7	$247.47	8.363%	$268.1659	$268.17	$268.15	$268.20
7 purchase totals =	$720.07		$791.6935	$791.69	$791.70	$791.70