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	$137.67	5.385%	$145.0835	$145.08	$145.10	$145.10
Purchase #2	$99.70	9.868%	$109.5384	$109.54	$109.55	$109.50
Purchase #3	$62.96	4.453%	$65.7636	$65.76	$65.75	$65.80
Purchase #4	$66.29	8.517%	$71.9359	$71.94	$71.95	$71.90
Purchase #5	$45.27	12.462%	$50.9115	$50.91	$50.90	$50.90
Purchase #6	$12.83	10.618%	$14.1923	$14.19	$14.20	$14.20
Purchase #7	$187.32	12.554%	$210.8362	$210.84	$210.85	$210.80
7 purchase totals =	$612.04		$668.2614	$668.26	$668.30	$668.20