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	$90.78	9.446%	$99.3551	$99.36	$99.35	$99.40
Purchase #2	$65.41	7.686%	$70.4374	$70.44	$70.45	$70.40
Purchase #3	$196.48	11.830%	$219.7236	$219.72	$219.70	$219.70
Purchase #4	$92.65	7.195%	$99.3162	$99.32	$99.30	$99.30
Purchase #5	$237.69	5.115%	$249.8478	$249.85	$249.85	$249.80
Purchase #6	$64.82	8.106%	$70.0743	$70.07	$70.05	$70.10
Purchase #7	$134.48	3.487%	$139.1693	$139.17	$139.15	$139.20
7 purchase totals =	$882.31		$947.9237	$947.93	$947.85	$947.90