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	$131.76	9.747%	$144.6026	$144.60	$144.60	$144.60
Purchase #2	$199.92	5.419%	$210.7537	$210.75	$210.75	$210.80
Purchase #3	$67.57	5.783%	$71.4776	$71.48	$71.50	$71.50
Purchase #4	$45.39	9.155%	$49.5455	$49.55	$49.55	$49.50
Purchase #5	$64.67	9.844%	$71.0361	$71.04	$71.05	$71.00
Purchase #6	$46.40	13.823%	$52.8139	$52.81	$52.80	$52.80
Purchase #7	$78.59	13.729%	$89.3796	$89.38	$89.40	$89.40
7 purchase totals =	$634.30		$689.6090	$689.61	$689.65	$689.60