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	$132.29	4.228%	$137.8832	$137.88	$137.90	$137.90
Purchase #2	$51.34	7.850%	$55.3702	$55.37	$55.35	$55.40
Purchase #3	$52.72	4.818%	$55.26	$55.26	$55.25	$55.30
Purchase #4	$90.60	10.810%	$100.3939	$100.39	$100.40	$100.40
Purchase #5	$7.68	5.631%	$8.1125	$8.11	$8.10	$8.10
Purchase #6	$188.36	10.340%	$207.8364	$207.84	$207.85	$207.80
Purchase #7	$139.61	8.144%	$150.9798	$150.98	$151.00	$151.00
7 purchase totals =	$662.60		$715.8360	$715.83	$715.85	$715.90