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	$179.77	4.366%	$187.6188	$187.62	$187.60	$187.60
Purchase #2	$240.63	13.773%	$273.772	$273.77	$273.75	$273.80
Purchase #3	$70.40	12.305%	$79.0627	$79.06	$79.05	$79.10
Purchase #4	$73.33	13.204%	$83.0125	$83.01	$83.00	$83.00
Purchase #5	$93.78	12.552%	$105.5513	$105.55	$105.55	$105.60
Purchase #6	$47.93	9.656%	$52.5581	$52.56	$52.55	$52.60
Purchase #7	$101.47	4.205%	$105.7368	$105.74	$105.75	$105.70
7 purchase totals =	$807.31		$887.3122	$887.31	$887.25	$887.40