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	$68.53	13.603%	$77.8521	$77.85	$77.85	$77.90
Purchase #2	$19.26	13.510%	$21.862	$21.86	$21.85	$21.90
Purchase #3	$71.89	10.393%	$79.3615	$79.36	$79.35	$79.40
Purchase #4	$10.62	3.576%	$10.9998	$11.00	$11.00	$11.00
Purchase #5	$82.38	10.464%	$91.0002	$91.00	$91.00	$91.00
Purchase #6	$188.96	4.181%	$196.8604	$196.86	$196.85	$196.90
Purchase #7	$41.60	3.273%	$42.9616	$42.96	$42.95	$43.00
7 purchase totals =	$483.24		$520.8976	$520.89	$520.85	$521.10