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	$25.60	13.864%	$29.1492	$29.15	$29.15	$29.10
Purchase #2	$173.38	10.495%	$191.5762	$191.58	$191.60	$191.60
Purchase #3	$19.59	13.424%	$22.2198	$22.22	$22.20	$22.20
Purchase #4	$54.81	9.137%	$59.818	$59.82	$59.80	$59.80
Purchase #5	$104.92	13.600%	$119.1891	$119.19	$119.20	$119.20
Purchase #6	$171.55	4.516%	$179.2972	$179.30	$179.30	$179.30
Purchase #7	$42.68	6.240%	$45.3432	$45.34	$45.35	$45.30
7 purchase totals =	$592.53		$646.5927	$646.60	$646.60	$646.50