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	$36.73	6.353%	$39.0635	$39.06	$39.05	$39.10
Purchase #2	$231.74	10.433%	$255.9174	$255.92	$255.90	$255.90
Purchase #3	$126.29	10.459%	$139.4987	$139.50	$139.50	$139.50
Purchase #4	$31.31	6.274%	$33.2744	$33.27	$33.25	$33.30
Purchase #5	$206.68	3.564%	$214.0461	$214.05	$214.05	$214.00
Purchase #6	$27.29	5.590%	$28.8155	$28.82	$28.80	$28.80
Purchase #7	$217.62	7.321%	$233.552	$233.55	$233.55	$233.60
7 purchase totals =	$877.66		$944.1676	$944.17	$944.10	$944.20