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	$99.66	4.692%	$104.336	$104.34	$104.35	$104.30
Purchase #2	$229.69	9.274%	$250.9915	$250.99	$251.00	$251.00
Purchase #3	$105.33	13.757%	$119.8202	$119.82	$119.80	$119.80
Purchase #4	$141.39	13.224%	$160.0874	$160.09	$160.10	$160.10
Purchase #5	$19.86	3.218%	$20.4991	$20.50	$20.50	$20.50
Purchase #6	$196.28	12.694%	$221.1958	$221.20	$221.20	$221.20
Purchase #7	$39.38	7.581%	$42.3654	$42.37	$42.35	$42.40
7 purchase totals =	$831.59		$919.2954	$919.31	$919.30	$919.30