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	$159.66	6.179%	$169.5254	$169.53	$169.55	$169.50
Purchase #2	$117.45	12.801%	$132.4848	$132.48	$132.50	$132.50
Purchase #3	$54.89	12.420%	$61.7073	$61.71	$61.70	$61.70
Purchase #4	$84.96	3.138%	$87.626	$87.63	$87.65	$87.60
Purchase #5	$249.90	13.146%	$282.7519	$282.75	$282.75	$282.80
Purchase #6	$103.70	7.818%	$111.8073	$111.81	$111.80	$111.80
Purchase #7	$101.57	10.177%	$111.9068	$111.91	$111.90	$111.90
7 purchase totals =	$872.13		$957.8095	$957.82	$957.85	$957.80