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	$22.86	8.463%	$24.7946	$24.79	$24.80	$24.80
Purchase #2	$203.46	9.119%	$222.0135	$222.01	$222.00	$222.00
Purchase #3	$188.86	8.747%	$205.3796	$205.38	$205.40	$205.40
Purchase #4	$10.40	13.109%	$11.7633	$11.76	$11.75	$11.80
Purchase #5	$203.60	9.829%	$223.6118	$223.61	$223.60	$223.60
Purchase #6	$49.80	8.471%	$54.0186	$54.02	$54.00	$54.00
Purchase #7	$234.52	9.517%	$256.8393	$256.84	$256.85	$256.80
7 purchase totals =	$913.50		$998.4207	$998.41	$998.40	$998.40