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	$117.64	12.124%	$131.9027	$131.90	$131.90	$131.90
Purchase #2	$139.30	11.635%	$155.5076	$155.51	$155.50	$155.50
Purchase #3	$96.29	13.668%	$109.4509	$109.45	$109.45	$109.50
Purchase #4	$102.84	10.118%	$113.2454	$113.25	$113.25	$113.20
Purchase #5	$58.77	3.805%	$61.0062	$61.01	$61.00	$61.00
Purchase #6	$52.62	5.575%	$55.5536	$55.55	$55.55	$55.60
Purchase #7	$152.99	13.206%	$173.1939	$173.19	$173.20	$173.20
7 purchase totals =	$720.45		$799.8603	$799.86	$799.85	$799.90