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	$67.81	13.162%	$76.7352	$76.74	$76.75	$76.70
Purchase #2	$212.99	13.424%	$241.5818	$241.58	$241.60	$241.60
Purchase #3	$153.41	10.754%	$169.9077	$169.91	$169.90	$169.90
Purchase #4	$208.27	7.298%	$223.4695	$223.47	$223.45	$223.50
Purchase #5	$11.55	13.127%	$13.0662	$13.07	$13.05	$13.10
Purchase #6	$51.55	4.415%	$53.8259	$53.83	$53.85	$53.80
Purchase #7	$52.96	6.181%	$56.2335	$56.23	$56.25	$56.20
7 purchase totals =	$758.54		$834.8198	$834.83	$834.85	$834.80