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	$147.42	11.502%	$164.3762	$164.38	$164.40	$164.40
Purchase #2	$147.63	4.334%	$154.0283	$154.03	$154.05	$154.00
Purchase #3	$139.76	3.438%	$144.5649	$144.56	$144.55	$144.60
Purchase #4	$87.38	3.624%	$90.5467	$90.55	$90.55	$90.50
Purchase #5	$60.79	4.833%	$63.728	$63.73	$63.75	$63.70
Purchase #6	$47.33	13.544%	$53.7404	$53.74	$53.75	$53.70
Purchase #7	$13.77	12.796%	$15.532	$15.53	$15.55	$15.50
7 purchase totals =	$644.08		$686.5165	$686.52	$686.60	$686.40