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	$153.48	4.790%	$160.8317	$160.83	$160.85	$160.80
Purchase #2	$142.45	7.768%	$153.5155	$153.52	$153.50	$153.50
Purchase #3	$37.72	12.446%	$42.4146	$42.41	$42.40	$42.40
Purchase #4	$132.47	8.176%	$143.3007	$143.30	$143.30	$143.30
Purchase #5	$179.73	12.282%	$201.8044	$201.80	$201.80	$201.80
Purchase #6	$153.41	12.321%	$172.3116	$172.31	$172.30	$172.30
Purchase #7	$61.89	11.640%	$69.094	$69.09	$69.10	$69.10
7 purchase totals =	$861.15		$943.2725	$943.26	$943.25	$943.20