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	$15.30	10.129%	$16.8497	$16.85	$16.85	$16.80
Purchase #2	$125.62	12.611%	$141.4619	$141.46	$141.45	$141.50
Purchase #3	$164.34	12.769%	$185.3246	$185.32	$185.30	$185.30
Purchase #4	$200.81	5.547%	$211.9489	$211.95	$211.95	$211.90
Purchase #5	$40.68	3.213%	$41.987	$41.99	$42.00	$42.00
Purchase #6	$57.57	8.191%	$62.2856	$62.29	$62.30	$62.30
Purchase #7	$127.76	10.578%	$141.2745	$141.27	$141.25	$141.30
7 purchase totals =	$732.08		$801.1322	$801.13	$801.10	$801.10