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	$11.74	6.288%	$12.4782	$12.48	$12.50	$12.50
Purchase #2	$14.43	4.418%	$15.0675	$15.07	$15.05	$15.10
Purchase #3	$52.91	3.363%	$54.6894	$54.69	$54.70	$54.70
Purchase #4	$229.41	6.760%	$244.9181	$244.92	$244.90	$244.90
Purchase #5	$155.35	7.167%	$166.4839	$166.48	$166.50	$166.50
Purchase #6	$52.59	4.284%	$54.843	$54.84	$54.85	$54.80
Purchase #7	$47.65	10.216%	$52.5179	$52.52	$52.50	$52.50
7 purchase totals =	$564.08		$600.9980	$601.00	$601.00	$601.00