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	$98.31	13.454%	$111.5366	$111.54	$111.55	$111.50
Purchase #2	$138.28	8.746%	$150.374	$150.37	$150.35	$150.40
Purchase #3	$8.72	9.144%	$9.5174	$9.52	$9.50	$9.50
Purchase #4	$29.38	9.405%	$32.1432	$32.14	$32.15	$32.10
Purchase #5	$81.49	9.813%	$89.4866	$89.49	$89.50	$89.50
Purchase #6	$83.88	13.340%	$95.0696	$95.07	$95.05	$95.10
Purchase #7	$206.61	12.662%	$232.771	$232.77	$232.75	$232.80
7 purchase totals =	$646.67		$720.8984	$720.90	$720.85	$720.90