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	$149.39	6.760%	$159.4888	$159.49	$159.50	$159.50
Purchase #2	$227.33	4.199%	$236.8756	$236.88	$236.90	$236.90
Purchase #3	$222.92	8.814%	$242.5682	$242.57	$242.55	$242.60
Purchase #4	$144.26	11.834%	$161.3317	$161.33	$161.35	$161.30
Purchase #5	$73.93	9.479%	$80.9378	$80.94	$80.95	$80.90
Purchase #6	$51.45	12.340%	$57.7989	$57.80	$57.80	$57.80
Purchase #7	$117.74	8.314%	$127.5289	$127.53	$127.55	$127.50
7 purchase totals =	$987.02		$1,066.5299	$1,066.54	$1,066.60	$1,066.50