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	$81.64	6.103%	$86.6225	$86.62	$86.60	$86.60
Purchase #2	$109.41	13.597%	$124.2865	$124.29	$124.30	$124.30
Purchase #3	$109.48	13.497%	$124.2565	$124.26	$124.25	$124.30
Purchase #4	$76.31	3.160%	$78.7214	$78.72	$78.70	$78.70
Purchase #5	$88.98	8.385%	$96.441	$96.44	$96.45	$96.40
Purchase #6	$145.57	3.682%	$150.9299	$150.93	$150.95	$150.90
Purchase #7	$211.92	8.696%	$230.3486	$230.35	$230.35	$230.30
7 purchase totals =	$823.31		$891.6064	$891.61	$891.60	$891.50