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	$102.90	6.345%	$109.429	$109.43	$109.45	$109.40
Purchase #2	$156.42	13.872%	$178.1186	$178.12	$178.10	$178.10
Purchase #3	$81.86	5.178%	$86.0987	$86.10	$86.10	$86.10
Purchase #4	$121.41	5.106%	$127.6092	$127.61	$127.60	$127.60
Purchase #5	$186.71	6.762%	$199.3353	$199.34	$199.35	$199.30
Purchase #6	$240.26	3.117%	$247.7489	$247.75	$247.75	$247.70
Purchase #7	$41.46	9.330%	$45.3282	$45.33	$45.35	$45.30
7 purchase totals =	$931.02		$993.6679	$993.68	$993.70	$993.50