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	$143.96	8.828%	$156.6688	$156.67	$156.65	$156.70
Purchase #2	$202.75	12.161%	$227.4064	$227.41	$227.40	$227.40
Purchase #3	$195.46	11.336%	$217.6173	$217.62	$217.60	$217.60
Purchase #4	$221.77	6.429%	$236.0276	$236.03	$236.05	$236.00
Purchase #5	$190.59	7.225%	$204.3601	$204.36	$204.35	$204.40
Purchase #6	$48.92	10.695%	$54.152	$54.15	$54.15	$54.20
Purchase #7	$48.34	12.371%	$54.3201	$54.32	$54.30	$54.30
7 purchase totals =	$1,051.79		$1,150.5523	$1,150.56	$1,150.50	$1,150.60