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	$83.34	3.405%	$86.1777	$86.18	$86.20	$86.20
Purchase #2	$165.62	11.464%	$184.6067	$184.61	$184.60	$184.60
Purchase #3	$144.34	6.740%	$154.0685	$154.07	$154.05	$154.10
Purchase #4	$51.84	6.275%	$55.093	$55.09	$55.10	$55.10
Purchase #5	$62.86	5.718%	$66.4543	$66.45	$66.45	$66.50
Purchase #6	$180.34	8.829%	$196.2622	$196.26	$196.25	$196.30
Purchase #7	$148.41	12.650%	$167.1839	$167.18	$167.20	$167.20
7 purchase totals =	$836.75		$909.8463	$909.84	$909.85	$910.00