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	$11.27	10.616%	$12.4664	$12.47	$12.45	$12.50
Purchase #2	$178.65	8.292%	$193.4637	$193.46	$193.45	$193.50
Purchase #3	$50.49	8.714%	$54.8897	$54.89	$54.90	$54.90
Purchase #4	$46.63	9.824%	$51.2109	$51.21	$51.20	$51.20
Purchase #5	$48.56	10.630%	$53.7219	$53.72	$53.70	$53.70
Purchase #6	$71.39	10.455%	$78.8538	$78.85	$78.85	$78.90
Purchase #7	$202.84	10.790%	$224.7264	$224.73	$224.75	$224.70
7 purchase totals =	$609.83		$669.3328	$669.33	$669.30	$669.40