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	$234.67	12.647%	$264.3487	$264.35	$264.35	$264.30
Purchase #2	$18.69	10.205%	$20.5973	$20.60	$20.60	$20.60
Purchase #3	$168.94	13.384%	$191.5509	$191.55	$191.55	$191.60
Purchase #4	$24.83	10.642%	$27.4724	$27.47	$27.45	$27.50
Purchase #5	$159.59	8.585%	$173.2908	$173.29	$173.30	$173.30
Purchase #6	$96.86	13.594%	$110.0271	$110.03	$110.05	$110.00
Purchase #7	$61.98	7.854%	$66.8479	$66.85	$66.85	$66.80
7 purchase totals =	$765.56		$854.1351	$854.14	$854.15	$854.10