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	$123.78	3.314%	$127.8821	$127.88	$127.90	$127.90
Purchase #2	$246.45	9.256%	$269.2614	$269.26	$269.25	$269.30
Purchase #3	$159.39	5.613%	$168.3366	$168.34	$168.35	$168.30
Purchase #4	$75.90	10.388%	$83.7845	$83.78	$83.80	$83.80
Purchase #5	$148.34	3.850%	$154.0511	$154.05	$154.05	$154.10
Purchase #6	$109.94	7.256%	$117.9172	$117.92	$117.90	$117.90
Purchase #7	$185.75	4.444%	$194.0047	$194.00	$194.00	$194.00
7 purchase totals =	$1,049.55		$1,115.2376	$1,115.23	$1,115.25	$1,115.30