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	$25.31	11.463%	$28.2113	$28.21	$28.20	$28.20
Purchase #2	$46.28	12.626%	$52.1233	$52.12	$52.10	$52.10
Purchase #3	$200.83	8.863%	$218.6296	$218.63	$218.65	$218.60
Purchase #4	$71.29	12.458%	$80.1713	$80.17	$80.15	$80.20
Purchase #5	$124.61	5.342%	$131.2667	$131.27	$131.25	$131.30
Purchase #6	$214.97	11.843%	$240.4289	$240.43	$240.45	$240.40
Purchase #7	$76.27	5.668%	$80.593	$80.59	$80.60	$80.60
7 purchase totals =	$759.56		$831.4241	$831.42	$831.40	$831.40