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	$98.38	13.260%	$111.4252	$111.43	$111.45	$111.40
Purchase #2	$63.50	11.863%	$71.033	$71.03	$71.05	$71.00
Purchase #3	$7.41	10.573%	$8.1935	$8.19	$8.20	$8.20
Purchase #4	$166.98	8.384%	$180.9796	$180.98	$181.00	$181.00
Purchase #5	$235.72	10.559%	$260.6097	$260.61	$260.60	$260.60
Purchase #6	$77.57	10.223%	$85.5	$85.50	$85.50	$85.50
Purchase #7	$93.30	10.264%	$102.8763	$102.88	$102.90	$102.90
7 purchase totals =	$742.86		$820.6173	$820.62	$820.70	$820.60