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	$165.56	5.589%	$174.8131	$174.81	$174.80	$174.80
Purchase #2	$243.95	6.140%	$258.9285	$258.93	$258.95	$258.90
Purchase #3	$201.45	8.309%	$218.1885	$218.19	$218.20	$218.20
Purchase #4	$69.88	9.294%	$76.3746	$76.37	$76.35	$76.40
Purchase #5	$217.55	7.189%	$233.1897	$233.19	$233.20	$233.20
Purchase #6	$35.45	5.342%	$37.3437	$37.34	$37.35	$37.30
Purchase #7	$18.85	9.752%	$20.6883	$20.69	$20.70	$20.70
7 purchase totals =	$952.69		$1,019.5264	$1,019.52	$1,019.55	$1,019.50