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	$99.52	6.227%	$105.7171	$105.72	$105.70	$105.70
Purchase #2	$230.74	11.650%	$257.6212	$257.62	$257.60	$257.60
Purchase #3	$180.35	5.854%	$190.9077	$190.91	$190.90	$190.90
Purchase #4	$99.58	9.502%	$109.0421	$109.04	$109.05	$109.00
Purchase #5	$48.75	6.330%	$51.8359	$51.84	$51.85	$51.80
Purchase #6	$48.34	13.682%	$54.9539	$54.95	$54.95	$55.00
Purchase #7	$239.80	3.850%	$249.0323	$249.03	$249.05	$249.00
7 purchase totals =	$947.08		$1,019.1102	$1,019.11	$1,019.10	$1,019.00