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	$114.72	6.640%	$122.3374	$122.34	$122.35	$122.30
Purchase #2	$32.37	3.862%	$33.6201	$33.62	$33.60	$33.60
Purchase #3	$167.74	3.276%	$173.2352	$173.24	$173.25	$173.20
Purchase #4	$214.82	5.165%	$225.9155	$225.92	$225.90	$225.90
Purchase #5	$218.64	13.631%	$248.4428	$248.44	$248.45	$248.40
Purchase #6	$82.88	9.578%	$90.8182	$90.82	$90.80	$90.80
Purchase #7	$24.88	10.758%	$27.5566	$27.56	$27.55	$27.60
7 purchase totals =	$856.05		$921.9258	$921.94	$921.90	$921.80