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	$181.73	13.295%	$205.891	$205.89	$205.90	$205.90
Purchase #2	$157.72	12.252%	$177.0439	$177.04	$177.05	$177.00
Purchase #3	$141.58	7.597%	$152.3358	$152.34	$152.35	$152.30
Purchase #4	$128.89	11.719%	$143.9946	$143.99	$144.00	$144.00
Purchase #5	$149.83	12.318%	$168.2861	$168.29	$168.30	$168.30
Purchase #6	$28.80	5.520%	$30.3898	$30.39	$30.40	$30.40
Purchase #7	$142.59	11.425%	$158.8809	$158.88	$158.90	$158.90
7 purchase totals =	$931.14		$1,036.8221	$1,036.82	$1,036.90	$1,036.80