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	$104.59	11.468%	$116.5844	$116.58	$116.60	$116.60
Purchase #2	$77.75	5.779%	$82.2432	$82.24	$82.25	$82.20
Purchase #3	$117.78	10.698%	$130.3801	$130.38	$130.40	$130.40
Purchase #4	$149.55	12.110%	$167.6605	$167.66	$167.65	$167.70
Purchase #5	$55.78	6.306%	$59.2975	$59.30	$59.30	$59.30
Purchase #6	$232.55	11.171%	$258.5282	$258.53	$258.55	$258.50
Purchase #7	$35.43	12.795%	$39.9633	$39.96	$39.95	$40.00
7 purchase totals =	$773.43		$854.6572	$854.65	$854.70	$854.70