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	$111.54	8.698%	$121.2417	$121.24	$121.25	$121.20
Purchase #2	$19.75	5.222%	$20.7813	$20.78	$20.80	$20.80
Purchase #3	$37.88	13.115%	$42.848	$42.85	$42.85	$42.80
Purchase #4	$180.26	9.128%	$196.7141	$196.71	$196.70	$196.70
Purchase #5	$69.31	3.498%	$71.7345	$71.73	$71.75	$71.70
Purchase #6	$167.48	8.341%	$181.4495	$181.45	$181.45	$181.40
Purchase #7	$117.78	12.679%	$132.7133	$132.71	$132.70	$132.70
7 purchase totals =	$704.00		$767.4824	$767.47	$767.50	$767.30