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	$182.61	3.423%	$188.8607	$188.86	$188.85	$188.90
Purchase #2	$81.99	4.384%	$85.5844	$85.58	$85.60	$85.60
Purchase #3	$167.64	4.232%	$174.7345	$174.73	$174.75	$174.70
Purchase #4	$37.53	6.667%	$40.0321	$40.03	$40.05	$40.00
Purchase #5	$149.92	12.718%	$168.9868	$168.99	$169.00	$169.00
Purchase #6	$91.39	5.155%	$96.1012	$96.10	$96.10	$96.10
Purchase #7	$52.29	13.298%	$59.2435	$59.24	$59.25	$59.20
7 purchase totals =	$763.37		$813.5432	$813.53	$813.60	$813.50