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	$125.95	8.601%	$136.783	$136.78	$136.80	$136.80
Purchase #2	$179.81	5.724%	$190.1023	$190.10	$190.10	$190.10
Purchase #3	$179.48	13.228%	$203.2216	$203.22	$203.20	$203.20
Purchase #4	$190.48	10.446%	$210.3775	$210.38	$210.40	$210.40
Purchase #5	$105.45	8.378%	$114.2846	$114.28	$114.30	$114.30
Purchase #6	$169.38	12.158%	$189.9732	$189.97	$189.95	$190.00
Purchase #7	$73.71	6.643%	$78.6066	$78.61	$78.60	$78.60
7 purchase totals =	$1,024.26		$1,123.3488	$1,123.34	$1,123.35	$1,123.40