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	$155.40	3.117%	$160.2438	$160.24	$160.25	$160.20
Purchase #2	$170.65	6.427%	$181.6177	$181.62	$181.60	$181.60
Purchase #3	$176.70	6.484%	$188.1572	$188.16	$188.15	$188.20
Purchase #4	$91.83	5.870%	$97.2204	$97.22	$97.20	$97.20
Purchase #5	$116.56	3.710%	$120.8844	$120.88	$120.90	$120.90
Purchase #6	$223.52	8.181%	$241.8062	$241.81	$241.80	$241.80
Purchase #7	$83.56	8.664%	$90.7996	$90.80	$90.80	$90.80
7 purchase totals =	$1,018.22		$1,080.7293	$1,080.73	$1,080.70	$1,080.70