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	$74.50	8.110%	$80.542	$80.54	$80.55	$80.50
Purchase #2	$208.73	5.108%	$219.3919	$219.39	$219.40	$219.40
Purchase #3	$82.69	9.709%	$90.7184	$90.72	$90.70	$90.70
Purchase #4	$76.91	6.836%	$82.1676	$82.17	$82.15	$82.20
Purchase #5	$235.26	8.464%	$255.1724	$255.17	$255.15	$255.20
Purchase #6	$67.70	5.327%	$71.3064	$71.31	$71.30	$71.30
Purchase #7	$94.39	9.497%	$103.3542	$103.35	$103.35	$103.40
7 purchase totals =	$840.18		$902.6529	$902.65	$902.60	$902.70