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	$137.42	3.417%	$142.1156	$142.12	$142.10	$142.10
Purchase #2	$121.68	3.470%	$125.9023	$125.90	$125.90	$125.90
Purchase #3	$228.64	10.725%	$253.1616	$253.16	$253.15	$253.20
Purchase #4	$84.91	5.506%	$89.5851	$89.59	$89.60	$89.60
Purchase #5	$121.81	7.780%	$131.2868	$131.29	$131.30	$131.30
Purchase #6	$38.59	13.490%	$43.7958	$43.80	$43.80	$43.80
Purchase #7	$31.39	10.425%	$34.6624	$34.66	$34.65	$34.70
7 purchase totals =	$764.44		$820.5096	$820.52	$820.50	$820.60