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	$18.84	8.660%	$20.4715	$20.47	$20.45	$20.50
Purchase #2	$196.71	13.219%	$222.7131	$222.71	$222.70	$222.70
Purchase #3	$194.51	13.408%	$220.5899	$220.59	$220.60	$220.60
Purchase #4	$207.53	12.822%	$234.1395	$234.14	$234.15	$234.10
Purchase #5	$75.99	3.253%	$78.462	$78.46	$78.45	$78.50
Purchase #6	$27.41	6.259%	$29.1256	$29.13	$29.15	$29.10
Purchase #7	$150.90	7.484%	$162.1934	$162.19	$162.20	$162.20
7 purchase totals =	$871.89		$967.6950	$967.69	$967.70	$967.70