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	$122.62	13.671%	$139.3834	$139.38	$139.40	$139.40
Purchase #2	$114.76	3.315%	$118.5643	$118.56	$118.55	$118.60
Purchase #3	$203.88	11.607%	$227.5444	$227.54	$227.55	$227.50
Purchase #4	$120.56	12.808%	$136.0013	$136.00	$136.00	$136.00
Purchase #5	$149.52	9.814%	$164.1939	$164.19	$164.20	$164.20
Purchase #6	$79.43	12.604%	$89.4414	$89.44	$89.45	$89.40
Purchase #7	$161.56	11.176%	$179.6159	$179.62	$179.60	$179.60
7 purchase totals =	$952.33		$1,054.7446	$1,054.73	$1,054.75	$1,054.70