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	$45.77	7.438%	$49.1744	$49.17	$49.15	$49.20
Purchase #2	$96.82	3.210%	$99.9279	$99.93	$99.95	$99.90
Purchase #3	$241.86	4.657%	$253.1234	$253.12	$253.10	$253.10
Purchase #4	$82.69	12.763%	$93.2437	$93.24	$93.25	$93.20
Purchase #5	$80.85	13.598%	$91.844	$91.84	$91.85	$91.80
Purchase #6	$97.46	12.473%	$109.6162	$109.62	$109.60	$109.60
Purchase #7	$85.82	8.107%	$92.7774	$92.78	$92.80	$92.80
7 purchase totals =	$731.27		$789.7070	$789.70	$789.70	$789.60