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	$81.88	10.659%	$90.6076	$90.61	$90.60	$90.60
Purchase #2	$172.81	13.569%	$196.2586	$196.26	$196.25	$196.30
Purchase #3	$162.28	8.332%	$175.8012	$175.80	$175.80	$175.80
Purchase #4	$174.34	11.412%	$194.2357	$194.24	$194.25	$194.20
Purchase #5	$220.73	7.125%	$236.457	$236.46	$236.45	$236.50
Purchase #6	$189.84	10.666%	$210.0883	$210.09	$210.10	$210.10
Purchase #7	$38.66	13.493%	$43.8764	$43.88	$43.90	$43.90
7 purchase totals =	$1,040.54		$1,147.3248	$1,147.34	$1,147.35	$1,147.40