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	$17.56	5.779%	$18.5748	$18.57	$18.55	$18.60
Purchase #2	$92.35	9.693%	$101.3015	$101.30	$101.30	$101.30
Purchase #3	$152.43	9.672%	$167.173	$167.17	$167.15	$167.20
Purchase #4	$239.85	9.467%	$262.5566	$262.56	$262.55	$262.60
Purchase #5	$108.54	11.387%	$120.8994	$120.90	$120.90	$120.90
Purchase #6	$144.82	6.442%	$154.1493	$154.15	$154.15	$154.10
Purchase #7	$9.84	4.811%	$10.3134	$10.31	$10.30	$10.30
7 purchase totals =	$765.39		$834.9680	$834.96	$834.90	$835.00