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	$74.86	4.569%	$78.2804	$78.28	$78.30	$78.30
Purchase #2	$94.60	4.835%	$99.1739	$99.17	$99.15	$99.20
Purchase #3	$102.47	5.575%	$108.1827	$108.18	$108.20	$108.20
Purchase #4	$85.36	11.868%	$95.4905	$95.49	$95.50	$95.50
Purchase #5	$117.96	4.645%	$123.4392	$123.44	$123.45	$123.40
Purchase #6	$143.84	5.144%	$151.2391	$151.24	$151.25	$151.20
Purchase #7	$25.89	4.553%	$27.0688	$27.07	$27.05	$27.10
7 purchase totals =	$644.98		$682.8746	$682.87	$682.90	$682.90