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	$137.89	13.542%	$156.5631	$156.56	$156.55	$156.60
Purchase #2	$97.48	11.466%	$108.6571	$108.66	$108.65	$108.70
Purchase #3	$90.76	7.768%	$97.8102	$97.81	$97.80	$97.80
Purchase #4	$191.90	12.314%	$215.5306	$215.53	$215.55	$215.50
Purchase #5	$72.25	12.314%	$81.1469	$81.15	$81.15	$81.10
Purchase #6	$181.46	10.292%	$200.1359	$200.14	$200.15	$200.10
Purchase #7	$151.73	10.788%	$168.0986	$168.10	$168.10	$168.10
7 purchase totals =	$923.47		$1,027.9424	$1,027.95	$1,027.95	$1,027.90