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	$21.74	11.464%	$24.2323	$24.23	$24.25	$24.20
Purchase #2	$93.67	10.425%	$103.4351	$103.44	$103.45	$103.40
Purchase #3	$196.81	13.601%	$223.5781	$223.58	$223.60	$223.60
Purchase #4	$110.57	6.260%	$117.4917	$117.49	$117.50	$117.50
Purchase #5	$68.66	5.229%	$72.2502	$72.25	$72.25	$72.30
Purchase #6	$229.42	12.373%	$257.8061	$257.81	$257.80	$257.80
Purchase #7	$50.44	3.532%	$52.2215	$52.22	$52.20	$52.20
7 purchase totals =	$771.31		$851.0150	$851.02	$851.05	$851.00