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	$54.75	3.122%	$56.4593	$56.46	$56.45	$56.50
Purchase #2	$73.64	6.715%	$78.5849	$78.58	$78.60	$78.60
Purchase #3	$7.32	8.125%	$7.9148	$7.91	$7.90	$7.90
Purchase #4	$177.30	3.812%	$184.0587	$184.06	$184.05	$184.10
Purchase #5	$85.81	8.816%	$93.375	$93.38	$93.40	$93.40
Purchase #6	$234.49	8.767%	$255.0477	$255.05	$255.05	$255.00
Purchase #7	$150.45	8.147%	$162.7072	$162.71	$162.70	$162.70
7 purchase totals =	$783.76		$838.1476	$838.15	$838.15	$838.20