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	$238.26	7.829%	$256.9134	$256.91	$256.90	$256.90
Purchase #2	$221.35	3.850%	$229.872	$229.87	$229.85	$229.90
Purchase #3	$42.58	7.702%	$45.8595	$45.86	$45.85	$45.90
Purchase #4	$171.57	6.169%	$182.1542	$182.15	$182.15	$182.20
Purchase #5	$60.92	9.292%	$66.5807	$66.58	$66.60	$66.60
Purchase #6	$211.36	11.384%	$235.4212	$235.42	$235.40	$235.40
Purchase #7	$100.83	4.721%	$105.5902	$105.59	$105.60	$105.60
7 purchase totals =	$1,046.87		$1,122.3912	$1,122.38	$1,122.35	$1,122.50