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	$40.48	4.365%	$42.247	$42.25	$42.25	$42.20
Purchase #2	$103.89	10.599%	$114.9013	$114.90	$114.90	$114.90
Purchase #3	$122.28	9.224%	$133.5591	$133.56	$133.55	$133.60
Purchase #4	$14.77	12.615%	$16.6332	$16.63	$16.65	$16.60
Purchase #5	$95.76	4.144%	$99.7283	$99.73	$99.75	$99.70
Purchase #6	$33.99	4.872%	$35.646	$35.65	$35.65	$35.60
Purchase #7	$160.38	3.430%	$165.881	$165.88	$165.90	$165.90
7 purchase totals =	$571.55		$608.5959	$608.60	$608.65	$608.50