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	$42.53	3.300%	$43.9335	$43.93	$43.95	$43.90
Purchase #2	$176.66	6.291%	$187.7737	$187.77	$187.75	$187.80
Purchase #3	$240.54	8.335%	$260.589	$260.59	$260.60	$260.60
Purchase #4	$164.25	7.325%	$176.2813	$176.28	$176.30	$176.30
Purchase #5	$48.27	11.559%	$53.8495	$53.85	$53.85	$53.80
Purchase #6	$63.30	11.839%	$70.7941	$70.79	$70.80	$70.80
Purchase #7	$34.87	6.564%	$37.1589	$37.16	$37.15	$37.20
7 purchase totals =	$770.42		$830.3800	$830.37	$830.40	$830.40