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	$33.97	9.273%	$37.12	$37.12	$37.10	$37.10
Purchase #2	$217.91	11.245%	$242.414	$242.41	$242.40	$242.40
Purchase #3	$52.72	9.263%	$57.6035	$57.60	$57.60	$57.60
Purchase #4	$176.71	6.667%	$188.4913	$188.49	$188.50	$188.50
Purchase #5	$127.37	5.640%	$134.5537	$134.55	$134.55	$134.60
Purchase #6	$113.67	8.280%	$123.0819	$123.08	$123.10	$123.10
Purchase #7	$104.26	13.573%	$118.4112	$118.41	$118.40	$118.40
7 purchase totals =	$826.61		$901.6756	$901.66	$901.65	$901.70