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	$102.73	9.455%	$112.4431	$112.44	$112.45	$112.40
Purchase #2	$127.72	11.276%	$142.1217	$142.12	$142.10	$142.10
Purchase #3	$45.77	13.296%	$51.8556	$51.86	$51.85	$51.90
Purchase #4	$168.96	13.489%	$191.751	$191.75	$191.75	$191.80
Purchase #5	$17.70	9.238%	$19.3351	$19.34	$19.35	$19.30
Purchase #6	$12.86	5.157%	$13.5232	$13.52	$13.50	$13.50
Purchase #7	$132.45	6.122%	$140.5586	$140.56	$140.55	$140.60
7 purchase totals =	$608.19		$671.5883	$671.59	$671.55	$671.60