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	$91.84	12.421%	$103.2474	$103.25	$103.25	$103.20
Purchase #2	$130.97	10.780%	$145.0886	$145.09	$145.10	$145.10
Purchase #3	$167.40	8.488%	$181.6089	$181.61	$181.60	$181.60
Purchase #4	$41.70	9.190%	$45.5322	$45.53	$45.55	$45.50
Purchase #5	$179.98	7.117%	$192.7892	$192.79	$192.80	$192.80
Purchase #6	$84.77	7.182%	$90.8582	$90.86	$90.85	$90.90
Purchase #7	$207.93	10.795%	$230.376	$230.38	$230.40	$230.40
7 purchase totals =	$904.59		$989.5005	$989.51	$989.55	$989.50