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	$231.77	11.522%	$258.4745	$258.47	$258.45	$258.50
Purchase #2	$124.33	5.823%	$131.5697	$131.57	$131.55	$131.60
Purchase #3	$233.27	3.116%	$240.5387	$240.54	$240.55	$240.50
Purchase #4	$58.94	5.718%	$62.3102	$62.31	$62.30	$62.30
Purchase #5	$50.27	8.665%	$54.6259	$54.63	$54.65	$54.60
Purchase #6	$243.94	3.503%	$252.4852	$252.49	$252.50	$252.50
Purchase #7	$97.51	3.216%	$100.6459	$100.65	$100.65	$100.60
7 purchase totals =	$1,040.03		$1,100.6501	$1,100.66	$1,100.65	$1,100.60