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	$188.33	8.739%	$204.7882	$204.79	$204.80	$204.80
Purchase #2	$228.82	11.164%	$254.3655	$254.37	$254.35	$254.40
Purchase #3	$232.57	7.586%	$250.2128	$250.21	$250.20	$250.20
Purchase #4	$18.79	12.493%	$21.1374	$21.14	$21.15	$21.10
Purchase #5	$117.52	5.466%	$123.9436	$123.94	$123.95	$123.90
Purchase #6	$216.71	10.692%	$239.8806	$239.88	$239.90	$239.90
Purchase #7	$34.52	7.224%	$37.0137	$37.01	$37.00	$37.00
7 purchase totals =	$1,037.26		$1,131.3418	$1,131.34	$1,131.35	$1,131.30