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	$79.85	11.659%	$89.1597	$89.16	$89.15	$89.20
Purchase #2	$139.64	6.658%	$148.9372	$148.94	$148.95	$148.90
Purchase #3	$37.96	4.376%	$39.6211	$39.62	$39.60	$39.60
Purchase #4	$105.49	10.352%	$116.4103	$116.41	$116.40	$116.40
Purchase #5	$29.74	7.640%	$32.0121	$32.01	$32.00	$32.00
Purchase #6	$120.27	10.149%	$132.4762	$132.48	$132.50	$132.50
Purchase #7	$180.88	3.370%	$186.9757	$186.98	$187.00	$187.00
7 purchase totals =	$693.83		$745.5923	$745.60	$745.60	$745.60