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	$148.80	12.456%	$167.3345	$167.33	$167.35	$167.30
Purchase #2	$81.38	10.109%	$89.6067	$89.61	$89.60	$89.60
Purchase #3	$26.71	8.573%	$28.9998	$29.00	$29.00	$29.00
Purchase #4	$38.64	8.503%	$41.9256	$41.93	$41.95	$41.90
Purchase #5	$81.28	9.428%	$88.9431	$88.94	$88.95	$88.90
Purchase #6	$87.69	4.507%	$91.6422	$91.64	$91.65	$91.60
Purchase #7	$9.31	13.493%	$10.5662	$10.57	$10.55	$10.60
7 purchase totals =	$473.81		$519.0181	$519.02	$519.05	$518.90