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	$71.45	9.468%	$78.2149	$78.21	$78.20	$78.20
Purchase #2	$187.56	6.412%	$199.5863	$199.59	$199.60	$199.60
Purchase #3	$74.38	6.737%	$79.391	$79.39	$79.40	$79.40
Purchase #4	$62.50	5.788%	$66.1175	$66.12	$66.10	$66.10
Purchase #5	$59.48	10.676%	$65.8301	$65.83	$65.85	$65.80
Purchase #6	$185.29	7.546%	$199.272	$199.27	$199.25	$199.30
Purchase #7	$108.86	13.753%	$123.8315	$123.83	$123.85	$123.80
7 purchase totals =	$749.52		$812.2433	$812.24	$812.25	$812.20