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	$24.94	8.283%	$27.0058	$27.01	$27.00	$27.00
Purchase #2	$188.78	13.332%	$213.9481	$213.95	$213.95	$213.90
Purchase #3	$19.90	6.626%	$21.2186	$21.22	$21.20	$21.20
Purchase #4	$156.34	11.502%	$174.3222	$174.32	$174.30	$174.30
Purchase #5	$90.93	10.400%	$100.3867	$100.39	$100.40	$100.40
Purchase #6	$59.78	3.417%	$61.8227	$61.82	$61.80	$61.80
Purchase #7	$103.73	10.774%	$114.9059	$114.91	$114.90	$114.90
7 purchase totals =	$644.40		$713.6100	$713.62	$713.55	$713.50