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	$148.82	12.613%	$167.5907	$167.59	$167.60	$167.60
Purchase #2	$145.51	11.281%	$161.925	$161.93	$161.95	$161.90
Purchase #3	$90.94	3.300%	$93.941	$93.94	$93.95	$93.90
Purchase #4	$31.58	10.164%	$34.7898	$34.79	$34.80	$34.80
Purchase #5	$24.91	9.155%	$27.1905	$27.19	$27.20	$27.20
Purchase #6	$38.28	6.633%	$40.8191	$40.82	$40.80	$40.80
Purchase #7	$5.95	10.243%	$6.5595	$6.56	$6.55	$6.60
7 purchase totals =	$485.99		$532.8156	$532.82	$532.85	$532.80