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	$103.89	6.437%	$110.5774	$110.58	$110.60	$110.60
Purchase #2	$44.52	6.301%	$47.3252	$47.33	$47.35	$47.30
Purchase #3	$214.93	8.631%	$233.4806	$233.48	$233.50	$233.50
Purchase #4	$88.97	6.663%	$94.8981	$94.90	$94.90	$94.90
Purchase #5	$67.58	5.553%	$71.3327	$71.33	$71.35	$71.30
Purchase #6	$117.49	8.561%	$127.5483	$127.55	$127.55	$127.50
Purchase #7	$121.50	7.154%	$130.1921	$130.19	$130.20	$130.20
7 purchase totals =	$758.88		$815.3544	$815.36	$815.45	$815.30