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	$136.45	11.134%	$151.6423	$151.64	$151.65	$151.60
Purchase #2	$83.25	13.253%	$94.2831	$94.28	$94.30	$94.30
Purchase #3	$103.61	5.697%	$109.5127	$109.51	$109.50	$109.50
Purchase #4	$102.99	5.469%	$108.6225	$108.62	$108.60	$108.60
Purchase #5	$88.29	6.737%	$94.2381	$94.24	$94.25	$94.20
Purchase #6	$150.26	6.861%	$160.5693	$160.57	$160.55	$160.60
Purchase #7	$93.30	10.310%	$102.9192	$102.92	$102.90	$102.90
7 purchase totals =	$758.15		$821.7872	$821.78	$821.75	$821.70