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	$96.33	6.826%	$102.9055	$102.91	$102.90	$102.90
Purchase #2	$172.89	4.300%	$180.3243	$180.32	$180.30	$180.30
Purchase #3	$37.34	12.691%	$42.0788	$42.08	$42.10	$42.10
Purchase #4	$71.28	7.312%	$76.492	$76.49	$76.50	$76.50
Purchase #5	$64.82	7.609%	$69.7522	$69.75	$69.75	$69.80
Purchase #6	$177.52	10.739%	$196.5839	$196.58	$196.60	$196.60
Purchase #7	$129.48	6.557%	$137.97	$137.97	$137.95	$138.00
7 purchase totals =	$749.66		$806.1067	$806.10	$806.10	$806.20