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	$116.52	13.484%	$132.2316	$132.23	$132.25	$132.20
Purchase #2	$185.92	10.172%	$204.8318	$204.83	$204.85	$204.80
Purchase #3	$102.43	12.247%	$114.9746	$114.97	$114.95	$115.00
Purchase #4	$32.68	7.645%	$35.1784	$35.18	$35.20	$35.20
Purchase #5	$39.89	6.123%	$42.3325	$42.33	$42.35	$42.30
Purchase #6	$131.41	11.179%	$146.1003	$146.10	$146.10	$146.10
Purchase #7	$37.55	6.743%	$40.082	$40.08	$40.10	$40.10
7 purchase totals =	$646.40		$715.7312	$715.72	$715.80	$715.70