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	$228.67	13.291%	$259.0625	$259.06	$259.05	$259.10
Purchase #2	$103.45	6.656%	$110.3356	$110.34	$110.35	$110.30
Purchase #3	$250.50	12.128%	$280.8806	$280.88	$280.90	$280.90
Purchase #4	$180.87	12.559%	$203.5855	$203.59	$203.60	$203.60
Purchase #5	$109.50	10.442%	$120.934	$120.93	$120.95	$120.90
Purchase #6	$169.88	7.516%	$182.6482	$182.65	$182.65	$182.60
Purchase #7	$36.66	6.269%	$38.9582	$38.96	$38.95	$39.00
7 purchase totals =	$1,079.53		$1,196.4046	$1,196.41	$1,196.45	$1,196.40