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	$19.30	6.363%	$20.5281	$20.53	$20.55	$20.50
Purchase #2	$74.97	4.520%	$78.3586	$78.36	$78.35	$78.40
Purchase #3	$126.78	6.398%	$134.8914	$134.89	$134.90	$134.90
Purchase #4	$61.96	12.130%	$69.4757	$69.48	$69.50	$69.50
Purchase #5	$17.42	4.455%	$18.1961	$18.20	$18.20	$18.20
Purchase #6	$83.73	12.758%	$94.4123	$94.41	$94.40	$94.40
Purchase #7	$48.38	8.647%	$52.5634	$52.56	$52.55	$52.60
7 purchase totals =	$432.54		$468.4256	$468.43	$468.45	$468.50