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	$17.81	13.405%	$20.1974	$20.20	$20.20	$20.20
Purchase #2	$72.31	10.585%	$79.964	$79.96	$79.95	$80.00
Purchase #3	$37.95	12.715%	$42.7753	$42.78	$42.80	$42.80
Purchase #4	$123.36	4.422%	$128.815	$128.82	$128.80	$128.80
Purchase #5	$167.83	12.429%	$188.6896	$188.69	$188.70	$188.70
Purchase #6	$215.30	13.480%	$244.3224	$244.32	$244.30	$244.30
Purchase #7	$78.87	3.429%	$81.5745	$81.57	$81.55	$81.60
7 purchase totals =	$713.43		$786.3382	$786.34	$786.30	$786.40