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	$74.25	5.149%	$78.0731	$78.07	$78.05	$78.10
Purchase #2	$104.71	6.407%	$111.4188	$111.42	$111.40	$111.40
Purchase #3	$86.62	8.419%	$93.9125	$93.91	$93.90	$93.90
Purchase #4	$133.38	6.705%	$142.3231	$142.32	$142.30	$142.30
Purchase #5	$39.96	8.628%	$43.4077	$43.41	$43.40	$43.40
Purchase #6	$225.31	8.846%	$245.2409	$245.24	$245.25	$245.20
Purchase #7	$111.65	4.610%	$116.7971	$116.80	$116.80	$116.80
7 purchase totals =	$775.88		$831.1732	$831.17	$831.10	$831.10