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	$138.60	11.698%	$154.8134	$154.81	$154.80	$154.80
Purchase #2	$190.75	5.148%	$200.5698	$200.57	$200.55	$200.60
Purchase #3	$138.72	3.820%	$144.0191	$144.02	$144.00	$144.00
Purchase #4	$186.66	12.548%	$210.0821	$210.08	$210.10	$210.10
Purchase #5	$57.91	5.813%	$61.2763	$61.28	$61.30	$61.30
Purchase #6	$140.58	11.779%	$157.1389	$157.14	$157.15	$157.10
Purchase #7	$138.37	10.275%	$152.5875	$152.59	$152.60	$152.60
7 purchase totals =	$991.59		$1,080.4871	$1,080.49	$1,080.50	$1,080.50