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	$104.57	13.350%	$118.5301	$118.53	$118.55	$118.50
Purchase #2	$212.43	3.860%	$220.6298	$220.63	$220.65	$220.60
Purchase #3	$137.45	10.523%	$151.9139	$151.91	$151.90	$151.90
Purchase #4	$52.47	3.522%	$54.318	$54.32	$54.30	$54.30
Purchase #5	$59.81	8.293%	$64.77	$64.77	$64.75	$64.80
Purchase #6	$6.57	10.412%	$7.2541	$7.25	$7.25	$7.30
Purchase #7	$46.78	13.872%	$53.2693	$53.27	$53.25	$53.30
7 purchase totals =	$620.08		$670.6852	$670.68	$670.65	$670.70