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	$145.52	10.268%	$160.462	$160.46	$160.45	$160.50
Purchase #2	$107.43	3.487%	$111.1761	$111.18	$111.20	$111.20
Purchase #3	$30.41	8.535%	$33.0055	$33.01	$33.00	$33.00
Purchase #4	$203.29	4.806%	$213.0601	$213.06	$213.05	$213.10
Purchase #5	$164.33	6.417%	$174.8751	$174.88	$174.90	$174.90
Purchase #6	$11.71	11.759%	$13.087	$13.09	$13.10	$13.10
Purchase #7	$90.90	4.331%	$94.8369	$94.84	$94.85	$94.80
7 purchase totals =	$753.59		$800.5027	$800.52	$800.55	$800.60