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	$33.62	5.682%	$35.5303	$35.53	$35.55	$35.50
Purchase #2	$203.98	8.746%	$221.8201	$221.82	$221.80	$221.80
Purchase #3	$134.60	4.468%	$140.6139	$140.61	$140.60	$140.60
Purchase #4	$50.84	9.409%	$55.6235	$55.62	$55.60	$55.60
Purchase #5	$80.47	11.627%	$89.8262	$89.83	$89.85	$89.80
Purchase #6	$153.30	11.370%	$170.7302	$170.73	$170.75	$170.70
Purchase #7	$211.42	4.712%	$221.3821	$221.38	$221.40	$221.40
7 purchase totals =	$868.23		$935.5263	$935.52	$935.55	$935.40