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	$136.86	4.181%	$142.5821	$142.58	$142.60	$142.60
Purchase #2	$49.82	9.831%	$54.7178	$54.72	$54.70	$54.70
Purchase #3	$37.91	12.657%	$42.7083	$42.71	$42.70	$42.70
Purchase #4	$110.72	6.126%	$117.5027	$117.50	$117.50	$117.50
Purchase #5	$31.30	10.648%	$34.6328	$34.63	$34.65	$34.60
Purchase #6	$175.61	13.777%	$199.8038	$199.80	$199.80	$199.80
Purchase #7	$131.64	8.357%	$142.6412	$142.64	$142.65	$142.60
7 purchase totals =	$673.86		$734.5887	$734.58	$734.60	$734.50