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	$224.74	12.103%	$251.9403	$251.94	$251.95	$251.90
Purchase #2	$53.96	11.271%	$60.0418	$60.04	$60.05	$60.00
Purchase #3	$72.32	13.694%	$82.2235	$82.22	$82.20	$82.20
Purchase #4	$113.90	10.856%	$126.265	$126.27	$126.25	$126.30
Purchase #5	$104.29	3.814%	$108.2676	$108.27	$108.25	$108.30
Purchase #6	$236.78	12.146%	$265.5393	$265.54	$265.55	$265.50
Purchase #7	$112.54	10.135%	$123.9459	$123.95	$123.95	$123.90
7 purchase totals =	$918.53		$1,018.2234	$1,018.23	$1,018.20	$1,018.10