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	$234.31	12.777%	$264.2478	$264.25	$264.25	$264.20
Purchase #2	$71.35	12.443%	$80.2281	$80.23	$80.25	$80.20
Purchase #3	$105.41	11.105%	$117.1158	$117.12	$117.10	$117.10
Purchase #4	$248.70	4.380%	$259.5931	$259.59	$259.60	$259.60
Purchase #5	$82.87	10.453%	$91.5324	$91.53	$91.55	$91.50
Purchase #6	$127.35	12.776%	$143.6202	$143.62	$143.60	$143.60
Purchase #7	$75.83	6.129%	$80.4776	$80.48	$80.50	$80.50
7 purchase totals =	$945.82		$1,036.8150	$1,036.82	$1,036.85	$1,036.70