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	$158.32	8.449%	$171.6965	$171.70	$171.70	$171.70
Purchase #2	$228.49	12.277%	$256.5417	$256.54	$256.55	$256.50
Purchase #3	$128.72	9.679%	$141.1788	$141.18	$141.20	$141.20
Purchase #4	$40.39	12.307%	$45.3608	$45.36	$45.35	$45.40
Purchase #5	$192.93	5.845%	$204.2068	$204.21	$204.20	$204.20
Purchase #6	$162.90	10.131%	$179.4034	$179.40	$179.40	$179.40
Purchase #7	$185.25	3.343%	$191.4429	$191.44	$191.45	$191.40
7 purchase totals =	$1,097.00		$1,189.8309	$1,189.83	$1,189.85	$1,189.80