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	$169.92	12.159%	$190.5806	$190.58	$190.60	$190.60
Purchase #2	$44.60	7.164%	$47.7951	$47.80	$47.80	$47.80
Purchase #3	$40.40	8.193%	$43.71	$43.71	$43.70	$43.70
Purchase #4	$16.31	10.332%	$17.9951	$18.00	$18.00	$18.00
Purchase #5	$86.76	6.570%	$92.4601	$92.46	$92.45	$92.50
Purchase #6	$6.37	12.746%	$7.1819	$7.18	$7.20	$7.20
Purchase #7	$48.50	11.570%	$54.1115	$54.11	$54.10	$54.10
7 purchase totals =	$412.86		$453.8343	$453.84	$453.85	$453.90