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	$192.54	12.139%	$215.9124	$215.91	$215.90	$215.90
Purchase #2	$111.44	5.470%	$117.5358	$117.54	$117.55	$117.50
Purchase #3	$109.29	10.272%	$120.5163	$120.52	$120.50	$120.50
Purchase #4	$190.66	9.560%	$208.8871	$208.89	$208.90	$208.90
Purchase #5	$27.86	6.415%	$29.6472	$29.65	$29.65	$29.60
Purchase #6	$112.65	13.459%	$127.8116	$127.81	$127.80	$127.80
Purchase #7	$40.88	13.409%	$46.3616	$46.36	$46.35	$46.40
7 purchase totals =	$785.32		$866.6720	$866.68	$866.65	$866.60