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	$37.47	12.470%	$42.1425	$42.14	$42.15	$42.10
Purchase #2	$145.89	4.744%	$152.811	$152.81	$152.80	$152.80
Purchase #3	$98.98	4.144%	$103.0817	$103.08	$103.10	$103.10
Purchase #4	$114.37	8.863%	$124.5066	$124.51	$124.50	$124.50
Purchase #5	$177.85	12.761%	$200.5454	$200.55	$200.55	$200.50
Purchase #6	$171.84	10.542%	$189.9554	$189.96	$189.95	$190.00
Purchase #7	$187.55	6.727%	$200.1665	$200.17	$200.15	$200.20
7 purchase totals =	$933.95		$1,013.2091	$1,013.22	$1,013.20	$1,013.20