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	$8.82	12.851%	$9.9535	$9.95	$9.95	$10.00
Purchase #2	$17.33	4.424%	$18.0967	$18.10	$18.10	$18.10
Purchase #3	$89.29	6.762%	$95.3278	$95.33	$95.35	$95.30
Purchase #4	$67.88	3.589%	$70.3162	$70.32	$70.30	$70.30
Purchase #5	$118.35	4.280%	$123.4154	$123.42	$123.40	$123.40
Purchase #6	$96.62	13.746%	$109.9014	$109.90	$109.90	$109.90
Purchase #7	$144.45	5.113%	$151.8357	$151.84	$151.85	$151.80
7 purchase totals =	$542.74		$578.8467	$578.86	$578.85	$578.80