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	$37.48	13.183%	$42.421	$42.42	$42.40	$42.40
Purchase #2	$87.34	8.161%	$94.4678	$94.47	$94.45	$94.50
Purchase #3	$132.74	8.726%	$144.3229	$144.32	$144.30	$144.30
Purchase #4	$31.60	10.686%	$34.9768	$34.98	$35.00	$35.00
Purchase #5	$19.88	5.458%	$20.9651	$20.97	$20.95	$21.00
Purchase #6	$180.26	9.117%	$196.6943	$196.69	$196.70	$196.70
Purchase #7	$198.46	7.857%	$214.053	$214.05	$214.05	$214.10
7 purchase totals =	$687.76		$747.9009	$747.90	$747.85	$748.00