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	$42.41	3.532%	$43.9079	$43.91	$43.90	$43.90
Purchase #2	$199.41	11.820%	$222.9803	$222.98	$223.00	$223.00
Purchase #3	$5.71	8.659%	$6.2044	$6.20	$6.20	$6.20
Purchase #4	$94.47	10.670%	$104.5499	$104.55	$104.55	$104.50
Purchase #5	$117.33	8.438%	$127.2303	$127.23	$127.25	$127.20
Purchase #6	$36.62	4.813%	$38.3825	$38.38	$38.40	$38.40
Purchase #7	$200.52	13.778%	$228.1476	$228.15	$228.15	$228.10
7 purchase totals =	$696.47		$771.4029	$771.40	$771.45	$771.30