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	$179.62	10.308%	$198.1352	$198.14	$198.15	$198.10
Purchase #2	$89.96	7.847%	$97.0192	$97.02	$97.00	$97.00
Purchase #3	$40.82	10.526%	$45.1167	$45.12	$45.10	$45.10
Purchase #4	$83.74	8.161%	$90.574	$90.57	$90.55	$90.60
Purchase #5	$169.34	5.287%	$178.293	$178.29	$178.30	$178.30
Purchase #6	$28.85	8.526%	$31.3098	$31.31	$31.30	$31.30
Purchase #7	$25.91	3.833%	$26.9031	$26.90	$26.90	$26.90
7 purchase totals =	$618.24		$667.3510	$667.35	$667.30	$667.30