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	$110.40	8.631%	$119.9286	$119.93	$119.95	$119.90
Purchase #2	$131.81	11.863%	$147.4466	$147.45	$147.45	$147.40
Purchase #3	$53.95	13.294%	$61.1221	$61.12	$61.10	$61.10
Purchase #4	$212.59	5.558%	$224.4058	$224.41	$224.40	$224.40
Purchase #5	$212.84	13.304%	$241.1562	$241.16	$241.15	$241.20
Purchase #6	$40.54	5.406%	$42.7316	$42.73	$42.75	$42.70
Purchase #7	$243.91	4.560%	$255.0323	$255.03	$255.05	$255.00
7 purchase totals =	$1,006.04		$1,091.8232	$1,091.83	$1,091.85	$1,091.70