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	$233.59	10.845%	$258.9228	$258.92	$258.90	$258.90
Purchase #2	$80.34	11.590%	$89.6514	$89.65	$89.65	$89.70
Purchase #3	$220.87	5.270%	$232.5098	$232.51	$232.50	$232.50
Purchase #4	$77.53	3.353%	$80.1296	$80.13	$80.15	$80.10
Purchase #5	$103.76	9.531%	$113.6494	$113.65	$113.65	$113.60
Purchase #6	$92.71	6.820%	$99.0328	$99.03	$99.05	$99.00
Purchase #7	$42.81	13.266%	$48.4892	$48.49	$48.50	$48.50
7 purchase totals =	$851.61		$922.3850	$922.38	$922.40	$922.30