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	$104.86	13.405%	$118.9165	$118.92	$118.90	$118.90
Purchase #2	$100.60	13.847%	$114.5301	$114.53	$114.55	$114.50
Purchase #3	$186.39	6.438%	$198.3898	$198.39	$198.40	$198.40
Purchase #4	$32.31	8.607%	$35.0909	$35.09	$35.10	$35.10
Purchase #5	$39.70	3.687%	$41.1637	$41.16	$41.15	$41.20
Purchase #6	$241.71	9.766%	$265.3154	$265.32	$265.30	$265.30
Purchase #7	$236.67	12.140%	$265.4017	$265.40	$265.40	$265.40
7 purchase totals =	$942.24		$1,038.8081	$1,038.81	$1,038.80	$1,038.80