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	$77.99	6.672%	$83.1935	$83.19	$83.20	$83.20
Purchase #2	$98.48	13.539%	$111.8132	$111.81	$111.80	$111.80
Purchase #3	$79.76	12.424%	$89.6694	$89.67	$89.65	$89.70
Purchase #4	$107.49	10.353%	$118.6184	$118.62	$118.60	$118.60
Purchase #5	$115.77	3.468%	$119.7849	$119.78	$119.80	$119.80
Purchase #6	$181.37	3.269%	$187.299	$187.30	$187.30	$187.30
Purchase #7	$141.28	3.703%	$146.5116	$146.51	$146.50	$146.50
7 purchase totals =	$802.14		$856.8900	$856.88	$856.85	$856.90