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	$52.64	7.317%	$56.4917	$56.49	$56.50	$56.50
Purchase #2	$33.47	7.178%	$35.8725	$35.87	$35.85	$35.90
Purchase #3	$72.78	9.332%	$79.5718	$79.57	$79.55	$79.60
Purchase #4	$117.45	8.799%	$127.7844	$127.78	$127.80	$127.80
Purchase #5	$23.54	4.678%	$24.6412	$24.64	$24.65	$24.60
Purchase #6	$244.52	11.459%	$272.5395	$272.54	$272.55	$272.50
Purchase #7	$226.71	5.377%	$238.9002	$238.90	$238.90	$238.90
7 purchase totals =	$771.11		$835.8013	$835.79	$835.80	$835.80