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	$11.89	13.621%	$13.5095	$13.51	$13.50	$13.50
Purchase #2	$222.65	5.442%	$234.7666	$234.77	$234.75	$234.80
Purchase #3	$138.37	7.590%	$148.8723	$148.87	$148.85	$148.90
Purchase #4	$165.46	12.635%	$186.3659	$186.37	$186.35	$186.40
Purchase #5	$203.68	3.805%	$211.43	$211.43	$211.45	$211.40
Purchase #6	$77.40	7.786%	$83.4264	$83.43	$83.45	$83.40
Purchase #7	$76.32	13.300%	$86.4706	$86.47	$86.45	$86.50
7 purchase totals =	$895.77		$964.8413	$964.85	$964.80	$964.90