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	$62.45	13.310%	$70.7621	$70.76	$70.75	$70.80
Purchase #2	$191.51	8.676%	$208.1254	$208.13	$208.15	$208.10
Purchase #3	$51.77	7.831%	$55.8241	$55.82	$55.80	$55.80
Purchase #4	$75.54	4.279%	$78.7724	$78.77	$78.75	$78.80
Purchase #5	$177.85	5.265%	$187.2138	$187.21	$187.20	$187.20
Purchase #6	$249.46	12.467%	$280.5602	$280.56	$280.55	$280.60
Purchase #7	$13.78	11.395%	$15.3502	$15.35	$15.35	$15.40
7 purchase totals =	$822.36		$896.6082	$896.60	$896.55	$896.70