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	$91.47	6.711%	$97.6086	$97.61	$97.60	$97.60
Purchase #2	$103.65	12.256%	$116.3533	$116.35	$116.35	$116.40
Purchase #3	$183.34	7.202%	$196.5441	$196.54	$196.55	$196.50
Purchase #4	$124.98	7.290%	$134.091	$134.09	$134.10	$134.10
Purchase #5	$70.32	13.665%	$79.9292	$79.93	$79.95	$79.90
Purchase #6	$129.71	11.406%	$144.5047	$144.50	$144.50	$144.50
Purchase #7	$46.63	8.203%	$50.4551	$50.46	$50.45	$50.50
7 purchase totals =	$750.10		$819.4860	$819.48	$819.50	$819.50