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	$117.32	13.831%	$133.5465	$133.55	$133.55	$133.50
Purchase #2	$153.78	10.508%	$169.9392	$169.94	$169.95	$169.90
Purchase #3	$84.26	4.626%	$88.1579	$88.16	$88.15	$88.20
Purchase #4	$84.54	5.454%	$89.1508	$89.15	$89.15	$89.20
Purchase #5	$209.98	9.790%	$230.537	$230.54	$230.55	$230.50
Purchase #6	$85.55	4.335%	$89.2586	$89.26	$89.25	$89.30
Purchase #7	$66.62	4.229%	$69.4374	$69.44	$69.45	$69.40
7 purchase totals =	$802.05		$870.0274	$870.04	$870.05	$870.00