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	$81.34	5.729%	$86	$86.00	$86.00	$86.00
Purchase #2	$40.30	7.134%	$43.175	$43.18	$43.20	$43.20
Purchase #3	$12.34	4.482%	$12.8931	$12.89	$12.90	$12.90
Purchase #4	$69.29	13.377%	$78.5589	$78.56	$78.55	$78.60
Purchase #5	$222.26	8.457%	$241.0565	$241.06	$241.05	$241.10
Purchase #6	$74.41	5.863%	$78.7727	$78.77	$78.75	$78.80
Purchase #7	$202.48	13.700%	$230.2198	$230.22	$230.20	$230.20
7 purchase totals =	$702.42		$770.6760	$770.68	$770.65	$770.80