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	$47.87	13.711%	$54.4335	$54.43	$54.45	$54.40
Purchase #2	$113.65	6.775%	$121.3498	$121.35	$121.35	$121.30
Purchase #3	$85.29	6.397%	$90.746	$90.75	$90.75	$90.70
Purchase #4	$144.59	10.154%	$159.2717	$159.27	$159.25	$159.30
Purchase #5	$165.79	9.874%	$182.1601	$182.16	$182.15	$182.20
Purchase #6	$77.41	4.228%	$80.6829	$80.68	$80.70	$80.70
Purchase #7	$136.69	4.260%	$142.513	$142.51	$142.50	$142.50
7 purchase totals =	$771.29		$831.1570	$831.15	$831.15	$831.10