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	$242.64	12.466%	$272.8875	$272.89	$272.90	$272.90
Purchase #2	$73.49	6.763%	$78.4601	$78.46	$78.45	$78.50
Purchase #3	$161.40	5.190%	$169.7767	$169.78	$169.80	$169.80
Purchase #4	$141.31	5.454%	$149.017	$149.02	$149.00	$149.00
Purchase #5	$216.33	4.822%	$226.7614	$226.76	$226.75	$226.80
Purchase #6	$59.76	13.455%	$67.8007	$67.80	$67.80	$67.80
Purchase #7	$17.46	8.212%	$18.8938	$18.89	$18.90	$18.90
7 purchase totals =	$912.39		$983.5972	$983.60	$983.60	$983.70