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	$37.60	12.562%	$42.3233	$42.32	$42.30	$42.30
Purchase #2	$47.84	11.254%	$53.2239	$53.22	$53.20	$53.20
Purchase #3	$87.64	13.682%	$99.6309	$99.63	$99.65	$99.60
Purchase #4	$206.47	13.650%	$234.6532	$234.65	$234.65	$234.70
Purchase #5	$205.37	4.208%	$214.012	$214.01	$214.00	$214.00
Purchase #6	$70.86	4.783%	$74.2492	$74.25	$74.25	$74.20
Purchase #7	$242.52	5.514%	$255.8926	$255.89	$255.90	$255.90
7 purchase totals =	$898.30		$973.9851	$973.97	$973.95	$973.90