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	$27.31	7.336%	$29.3135	$29.31	$29.30	$29.30
Purchase #2	$49.25	13.382%	$55.8406	$55.84	$55.85	$55.80
Purchase #3	$126.80	12.869%	$143.1179	$143.12	$143.10	$143.10
Purchase #4	$71.80	12.539%	$80.803	$80.80	$80.80	$80.80
Purchase #5	$176.89	7.626%	$190.3796	$190.38	$190.40	$190.40
Purchase #6	$134.27	12.231%	$150.6926	$150.69	$150.70	$150.70
Purchase #7	$70.25	10.276%	$77.4689	$77.47	$77.45	$77.50
7 purchase totals =	$656.57		$727.6161	$727.61	$727.60	$727.60