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	$220.29	3.535%	$228.0773	$228.08	$228.10	$228.10
Purchase #2	$244.56	5.770%	$258.6711	$258.67	$258.65	$258.70
Purchase #3	$186.57	11.804%	$208.5927	$208.59	$208.60	$208.60
Purchase #4	$223.67	6.788%	$238.8527	$238.85	$238.85	$238.90
Purchase #5	$142.55	7.131%	$152.7152	$152.72	$152.70	$152.70
Purchase #6	$153.53	9.347%	$167.8804	$167.88	$167.90	$167.90
Purchase #7	$56.73	6.158%	$60.2234	$60.22	$60.20	$60.20
7 purchase totals =	$1,227.90		$1,315.0128	$1,315.01	$1,315.00	$1,315.10