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	$39.93	7.771%	$43.033	$43.03	$43.05	$43.00
Purchase #2	$61.28	3.775%	$63.5933	$63.59	$63.60	$63.60
Purchase #3	$50.27	6.484%	$53.5295	$53.53	$53.55	$53.50
Purchase #4	$182.71	4.472%	$190.8808	$190.88	$190.90	$190.90
Purchase #5	$52.83	4.126%	$55.0098	$55.01	$55.00	$55.00
Purchase #6	$149.74	12.526%	$168.4964	$168.50	$168.50	$168.50
Purchase #7	$25.57	8.731%	$27.8025	$27.80	$27.80	$27.80
7 purchase totals =	$562.33		$602.3453	$602.34	$602.40	$602.30