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	$32.45	11.774%	$36.2707	$36.27	$36.25	$36.30
Purchase #2	$153.45	5.789%	$162.3332	$162.33	$162.35	$162.30
Purchase #3	$35.75	13.622%	$40.6199	$40.62	$40.60	$40.60
Purchase #4	$73.75	3.787%	$76.5429	$76.54	$76.55	$76.50
Purchase #5	$227.84	13.444%	$258.4708	$258.47	$258.45	$258.50
Purchase #6	$190.55	11.298%	$212.0783	$212.08	$212.10	$212.10
Purchase #7	$148.69	6.612%	$158.5214	$158.52	$158.50	$158.50
7 purchase totals =	$862.48		$944.8372	$944.83	$944.80	$944.80