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	$54.59	7.549%	$58.711	$58.71	$58.70	$58.70
Purchase #2	$126.40	10.648%	$139.8591	$139.86	$139.85	$139.90
Purchase #3	$89.77	3.511%	$92.9218	$92.92	$92.90	$92.90
Purchase #4	$126.30	8.666%	$137.2452	$137.25	$137.25	$137.20
Purchase #5	$29.80	13.617%	$33.8579	$33.86	$33.85	$33.90
Purchase #6	$12.33	13.603%	$14.0072	$14.01	$14.00	$14.00
Purchase #7	$74.68	6.813%	$79.7679	$79.77	$79.75	$79.80
7 purchase totals =	$513.87		$556.3701	$556.38	$556.30	$556.40