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	$209.35	6.332%	$222.606	$222.61	$222.60	$222.60
Purchase #2	$181.69	9.684%	$199.2849	$199.28	$199.30	$199.30
Purchase #3	$94.99	6.156%	$100.8376	$100.84	$100.85	$100.80
Purchase #4	$129.60	5.188%	$136.3236	$136.32	$136.30	$136.30
Purchase #5	$54.41	10.299%	$60.0137	$60.01	$60.00	$60.00
Purchase #6	$114.71	13.538%	$130.2394	$130.24	$130.25	$130.20
Purchase #7	$222.34	8.817%	$241.9437	$241.94	$241.95	$241.90
7 purchase totals =	$1,007.09		$1,091.2489	$1,091.24	$1,091.25	$1,091.10