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	$63.34	4.736%	$66.3398	$66.34	$66.35	$66.30
Purchase #2	$175.88	6.664%	$187.6006	$187.60	$187.60	$187.60
Purchase #3	$19.93	9.831%	$21.8893	$21.89	$21.90	$21.90
Purchase #4	$134.34	9.353%	$146.9048	$146.90	$146.90	$146.90
Purchase #5	$150.90	13.820%	$171.7544	$171.75	$171.75	$171.80
Purchase #6	$181.50	13.558%	$206.1078	$206.11	$206.10	$206.10
Purchase #7	$90.36	10.303%	$99.6698	$99.67	$99.65	$99.70
7 purchase totals =	$816.25		$900.2665	$900.26	$900.25	$900.30