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	$160.38	13.220%	$181.5822	$181.58	$181.60	$181.60
Purchase #2	$192.46	10.225%	$212.139	$212.14	$212.15	$212.10
Purchase #3	$16.48	13.291%	$18.6704	$18.67	$18.65	$18.70
Purchase #4	$171.66	8.854%	$186.8588	$186.86	$186.85	$186.90
Purchase #5	$196.76	13.290%	$222.9094	$222.91	$222.90	$222.90
Purchase #6	$243.56	5.492%	$256.9363	$256.94	$256.95	$256.90
Purchase #7	$44.67	8.779%	$48.5916	$48.59	$48.60	$48.60
7 purchase totals =	$1,025.97		$1,127.6877	$1,127.69	$1,127.70	$1,127.70