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	$90.38	9.804%	$99.2409	$99.24	$99.25	$99.20
Purchase #2	$101.83	12.406%	$114.463	$114.46	$114.45	$114.50
Purchase #3	$171.52	10.350%	$189.2723	$189.27	$189.25	$189.30
Purchase #4	$124.72	5.512%	$131.5946	$131.59	$131.60	$131.60
Purchase #5	$243.81	12.419%	$274.0888	$274.09	$274.10	$274.10
Purchase #6	$102.62	7.261%	$110.0712	$110.07	$110.05	$110.10
Purchase #7	$84.52	6.563%	$90.067	$90.07	$90.05	$90.10
7 purchase totals =	$919.40		$1,008.7978	$1,008.79	$1,008.75	$1,008.90