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	$94.73	6.470%	$100.859	$100.86	$100.85	$100.90
Purchase #2	$115.36	10.619%	$127.6101	$127.61	$127.60	$127.60
Purchase #3	$141.59	4.393%	$147.81	$147.81	$147.80	$147.80
Purchase #4	$93.91	7.487%	$100.941	$100.94	$100.95	$100.90
Purchase #5	$161.39	13.378%	$182.9808	$182.98	$183.00	$183.00
Purchase #6	$209.35	12.391%	$235.2906	$235.29	$235.30	$235.30
Purchase #7	$30.72	13.177%	$34.768	$34.77	$34.75	$34.80
7 purchase totals =	$847.05		$930.2595	$930.26	$930.25	$930.30