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	$22.83	6.768%	$24.3751	$24.38	$24.40	$24.40
Purchase #2	$204.93	12.490%	$230.5258	$230.53	$230.55	$230.50
Purchase #3	$78.43	10.429%	$86.6095	$86.61	$86.60	$86.60
Purchase #4	$106.45	13.528%	$120.8506	$120.85	$120.85	$120.90
Purchase #5	$64.26	5.729%	$67.9415	$67.94	$67.95	$67.90
Purchase #6	$111.82	6.622%	$119.2247	$119.22	$119.20	$119.20
Purchase #7	$88.35	3.259%	$91.2293	$91.23	$91.25	$91.20
7 purchase totals =	$677.07		$740.7565	$740.76	$740.80	$740.70