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	$28.70	9.456%	$31.4139	$31.41	$31.40	$31.40
Purchase #2	$86.64	10.701%	$95.9113	$95.91	$95.90	$95.90
Purchase #3	$248.66	4.767%	$260.5136	$260.51	$260.50	$260.50
Purchase #4	$83.57	10.783%	$92.5814	$92.58	$92.60	$92.60
Purchase #5	$193.78	9.698%	$212.5728	$212.57	$212.55	$212.60
Purchase #6	$158.83	3.544%	$164.4589	$164.46	$164.45	$164.50
Purchase #7	$156.55	11.165%	$174.0288	$174.03	$174.05	$174.00
7 purchase totals =	$956.73		$1,031.4807	$1,031.47	$1,031.45	$1,031.50