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	$198.50	6.236%	$210.8785	$210.88	$210.90	$210.90
Purchase #2	$177.51	8.677%	$192.9125	$192.91	$192.90	$192.90
Purchase #3	$107.37	8.795%	$116.8132	$116.81	$116.80	$116.80
Purchase #4	$130.84	11.678%	$146.1195	$146.12	$146.10	$146.10
Purchase #5	$221.63	10.122%	$244.0634	$244.06	$244.05	$244.10
Purchase #6	$43.30	9.626%	$47.4681	$47.47	$47.45	$47.50
Purchase #7	$81.72	9.660%	$89.6142	$89.61	$89.60	$89.60
7 purchase totals =	$960.87		$1,047.8694	$1,047.86	$1,047.80	$1,047.90