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	$208.91	10.669%	$231.1986	$231.20	$231.20	$231.20
Purchase #2	$173.75	3.535%	$179.8921	$179.89	$179.90	$179.90
Purchase #3	$117.96	5.853%	$124.8642	$124.86	$124.85	$124.90
Purchase #4	$58.79	12.865%	$66.3533	$66.35	$66.35	$66.40
Purchase #5	$25.91	9.156%	$28.2823	$28.28	$28.30	$28.30
Purchase #6	$227.25	12.584%	$255.8471	$255.85	$255.85	$255.80
Purchase #7	$227.83	11.610%	$254.2811	$254.28	$254.30	$254.30
7 purchase totals =	$1,040.40		$1,140.7187	$1,140.71	$1,140.75	$1,140.80