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	$166.67	8.525%	$180.8786	$180.88	$180.90	$180.90
Purchase #2	$144.66	12.363%	$162.5443	$162.54	$162.55	$162.50
Purchase #3	$48.66	4.312%	$50.7582	$50.76	$50.75	$50.80
Purchase #4	$94.25	11.860%	$105.4281	$105.43	$105.45	$105.40
Purchase #5	$134.53	8.182%	$145.5372	$145.54	$145.55	$145.50
Purchase #6	$210.69	12.167%	$236.3247	$236.32	$236.30	$236.30
Purchase #7	$99.49	11.840%	$111.2696	$111.27	$111.25	$111.30
7 purchase totals =	$898.95		$992.7407	$992.74	$992.75	$992.70