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	$29.94	11.398%	$33.3526	$33.35	$33.35	$33.40
Purchase #2	$121.60	3.510%	$125.8682	$125.87	$125.85	$125.90
Purchase #3	$122.70	13.294%	$139.0117	$139.01	$139.00	$139.00
Purchase #4	$138.47	10.424%	$152.9041	$152.90	$152.90	$152.90
Purchase #5	$94.40	5.816%	$99.8903	$99.89	$99.90	$99.90
Purchase #6	$32.45	8.471%	$35.1988	$35.20	$35.20	$35.20
Purchase #7	$233.98	6.813%	$249.9211	$249.92	$249.90	$249.90
7 purchase totals =	$773.54		$836.1468	$836.14	$836.10	$836.20