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	$121.82	9.487%	$133.3771	$133.38	$133.40	$133.40
Purchase #2	$116.85	7.841%	$126.0122	$126.01	$126.00	$126.00
Purchase #3	$212.40	10.175%	$234.0117	$234.01	$234.00	$234.00
Purchase #4	$37.42	7.622%	$40.2722	$40.27	$40.25	$40.30
Purchase #5	$102.89	13.586%	$116.8686	$116.87	$116.85	$116.90
Purchase #6	$102.76	11.650%	$114.7315	$114.73	$114.75	$114.70
Purchase #7	$18.54	9.597%	$20.3193	$20.32	$20.30	$20.30
7 purchase totals =	$712.68		$785.5926	$785.59	$785.55	$785.60