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	$27.74	6.403%	$29.5162	$29.52	$29.50	$29.50
Purchase #2	$128.54	11.397%	$143.1897	$143.19	$143.20	$143.20
Purchase #3	$199.56	4.317%	$208.175	$208.18	$208.20	$208.20
Purchase #4	$230.87	6.299%	$245.4125	$245.41	$245.40	$245.40
Purchase #5	$234.26	10.573%	$259.0283	$259.03	$259.05	$259.00
Purchase #6	$221.36	3.730%	$229.6167	$229.62	$229.60	$229.60
Purchase #7	$76.83	6.141%	$81.5481	$81.55	$81.55	$81.50
7 purchase totals =	$1,119.16		$1,196.4865	$1,196.50	$1,196.50	$1,196.40