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	$39.91	8.209%	$43.1862	$43.19	$43.20	$43.20
Purchase #2	$132.86	7.792%	$143.2125	$143.21	$143.20	$143.20
Purchase #3	$128.68	8.190%	$139.2189	$139.22	$139.20	$139.20
Purchase #4	$196.41	9.749%	$215.558	$215.56	$215.55	$215.60
Purchase #5	$59.53	4.378%	$62.1362	$62.14	$62.15	$62.10
Purchase #6	$157.89	5.397%	$166.4113	$166.41	$166.40	$166.40
Purchase #7	$181.68	10.298%	$200.3894	$200.39	$200.40	$200.40
7 purchase totals =	$896.96		$970.1125	$970.12	$970.10	$970.10