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	$248.27	6.568%	$264.5764	$264.58	$264.60	$264.60
Purchase #2	$72.89	12.503%	$82.0034	$82.00	$82.00	$82.00
Purchase #3	$77.35	5.614%	$81.6924	$81.69	$81.70	$81.70
Purchase #4	$228.77	13.840%	$260.4318	$260.43	$260.45	$260.40
Purchase #5	$153.44	9.392%	$167.8511	$167.85	$167.85	$167.90
Purchase #6	$162.58	8.711%	$176.7423	$176.74	$176.75	$176.70
Purchase #7	$149.28	11.705%	$166.7532	$166.75	$166.75	$166.80
7 purchase totals =	$1,092.58		$1,200.0506	$1,200.04	$1,200.10	$1,200.10