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	$91.94	10.738%	$101.8125	$101.81	$101.80	$101.80
Purchase #2	$208.88	3.698%	$216.6044	$216.60	$216.60	$216.60
Purchase #3	$50.72	6.104%	$53.8159	$53.82	$53.80	$53.80
Purchase #4	$6.50	5.771%	$6.8751	$6.88	$6.90	$6.90
Purchase #5	$208.90	9.250%	$228.2233	$228.22	$228.20	$228.20
Purchase #6	$67.28	8.365%	$72.908	$72.91	$72.90	$72.90
Purchase #7	$138.80	3.283%	$143.3568	$143.36	$143.35	$143.40
7 purchase totals =	$773.02		$823.5960	$823.60	$823.55	$823.60