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	$170.50	8.295%	$184.643	$184.64	$184.65	$184.60
Purchase #2	$138.55	11.787%	$154.8809	$154.88	$154.90	$154.90
Purchase #3	$140.26	5.524%	$148.008	$148.01	$148.00	$148.00
Purchase #4	$70.70	11.154%	$78.5859	$78.59	$78.60	$78.60
Purchase #5	$245.86	3.426%	$254.2832	$254.28	$254.30	$254.30
Purchase #6	$214.53	6.670%	$228.8392	$228.84	$228.85	$228.80
Purchase #7	$66.97	11.274%	$74.5202	$74.52	$74.50	$74.50
7 purchase totals =	$1,047.37		$1,123.7604	$1,123.76	$1,123.80	$1,123.70