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	$41.91	8.143%	$45.3227	$45.32	$45.30	$45.30
Purchase #2	$108.37	7.663%	$116.6744	$116.67	$116.65	$116.70
Purchase #3	$173.36	3.277%	$179.041	$179.04	$179.05	$179.00
Purchase #4	$234.61	10.215%	$258.5754	$258.58	$258.60	$258.60
Purchase #5	$47.43	3.111%	$48.9055	$48.91	$48.90	$48.90
Purchase #6	$19.49	7.328%	$20.9182	$20.92	$20.90	$20.90
Purchase #7	$83.59	7.555%	$89.9052	$89.91	$89.90	$89.90
7 purchase totals =	$708.76		$759.3424	$759.35	$759.30	$759.30