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	$33.97	9.404%	$37.1645	$37.16	$37.15	$37.20
Purchase #2	$152.47	6.295%	$162.068	$162.07	$162.05	$162.10
Purchase #3	$150.72	10.347%	$166.315	$166.32	$166.30	$166.30
Purchase #4	$171.63	13.548%	$194.8824	$194.88	$194.90	$194.90
Purchase #5	$159.94	3.765%	$165.9617	$165.96	$165.95	$166.00
Purchase #6	$12.97	4.867%	$13.6012	$13.60	$13.60	$13.60
Purchase #7	$34.86	7.487%	$37.47	$37.47	$37.45	$37.50
7 purchase totals =	$716.56		$777.4628	$777.46	$777.40	$777.60