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	$80.85	5.712%	$85.4682	$85.47	$85.45	$85.50
Purchase #2	$67.54	3.840%	$70.1335	$70.13	$70.15	$70.10
Purchase #3	$74.31	3.134%	$76.6389	$76.64	$76.65	$76.60
Purchase #4	$88.78	13.788%	$101.021	$101.02	$101.00	$101.00
Purchase #5	$86.39	10.249%	$95.2441	$95.24	$95.25	$95.20
Purchase #6	$173.83	11.848%	$194.4254	$194.43	$194.45	$194.40
Purchase #7	$16.89	9.205%	$18.4447	$18.44	$18.45	$18.40
7 purchase totals =	$588.59		$641.3758	$641.37	$641.40	$641.20