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	$189.55	5.809%	$200.561	$200.56	$200.55	$200.60
Purchase #2	$126.58	12.532%	$142.443	$142.44	$142.45	$142.40
Purchase #3	$127.32	7.465%	$136.8244	$136.82	$136.80	$136.80
Purchase #4	$24.82	3.225%	$25.6204	$25.62	$25.60	$25.60
Purchase #5	$50.65	9.422%	$55.4222	$55.42	$55.40	$55.40
Purchase #6	$220.95	6.792%	$235.9569	$235.96	$235.95	$236.00
Purchase #7	$38.67	12.394%	$43.4628	$43.46	$43.45	$43.50
7 purchase totals =	$778.54		$840.2907	$840.28	$840.20	$840.30