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	$73.91	9.677%	$81.0623	$81.06	$81.05	$81.10
Purchase #2	$162.28	8.617%	$176.2637	$176.26	$176.25	$176.30
Purchase #3	$171.33	8.438%	$185.7868	$185.79	$185.80	$185.80
Purchase #4	$176.25	11.311%	$196.1856	$196.19	$196.20	$196.20
Purchase #5	$132.69	8.443%	$143.893	$143.89	$143.90	$143.90
Purchase #6	$123.65	13.578%	$140.4392	$140.44	$140.45	$140.40
Purchase #7	$190.90	8.772%	$207.6457	$207.65	$207.65	$207.60
7 purchase totals =	$1,031.01		$1,131.2763	$1,131.28	$1,131.30	$1,131.30