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	$86.43	3.322%	$89.3012	$89.30	$89.30	$89.30
Purchase #2	$34.44	8.868%	$37.4941	$37.49	$37.50	$37.50
Purchase #3	$10.89	9.423%	$11.9162	$11.92	$11.90	$11.90
Purchase #4	$125.50	11.225%	$139.5874	$139.59	$139.60	$139.60
Purchase #5	$96.87	11.558%	$108.0662	$108.07	$108.05	$108.10
Purchase #6	$215.62	13.511%	$244.7524	$244.75	$244.75	$244.80
Purchase #7	$29.38	11.366%	$32.7193	$32.72	$32.70	$32.70
7 purchase totals =	$599.13		$663.8368	$663.84	$663.80	$663.90