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	$33.81	10.630%	$37.404	$37.40	$37.40	$37.40
Purchase #2	$189.83	4.633%	$198.6248	$198.62	$198.60	$198.60
Purchase #3	$189.51	13.646%	$215.3705	$215.37	$215.35	$215.40
Purchase #4	$237.31	5.704%	$250.8462	$250.85	$250.85	$250.80
Purchase #5	$59.79	10.592%	$66.123	$66.12	$66.10	$66.10
Purchase #6	$103.34	4.535%	$108.0265	$108.03	$108.05	$108.00
Purchase #7	$26.82	10.797%	$29.7158	$29.72	$29.70	$29.70
7 purchase totals =	$840.41		$906.1108	$906.11	$906.05	$906.00