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	$102.45	6.750%	$109.3654	$109.37	$109.35	$109.40
Purchase #2	$163.29	11.739%	$182.4586	$182.46	$182.45	$182.50
Purchase #3	$103.87	12.143%	$116.4829	$116.48	$116.50	$116.50
Purchase #4	$223.83	5.820%	$236.8569	$236.86	$236.85	$236.90
Purchase #5	$34.88	10.628%	$38.587	$38.59	$38.60	$38.60
Purchase #6	$64.61	9.753%	$70.9114	$70.91	$70.90	$70.90
Purchase #7	$201.78	10.175%	$222.3111	$222.31	$222.30	$222.30
7 purchase totals =	$894.71		$976.9733	$976.98	$976.95	$977.10