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	$202.42	11.506%	$225.7104	$225.71	$225.70	$225.70
Purchase #2	$126.35	13.476%	$143.3769	$143.38	$143.40	$143.40
Purchase #3	$44.48	13.450%	$50.4626	$50.46	$50.45	$50.50
Purchase #4	$202.98	4.255%	$211.6168	$211.62	$211.60	$211.60
Purchase #5	$65.72	8.163%	$71.0847	$71.08	$71.10	$71.10
Purchase #6	$122.79	7.248%	$131.6898	$131.69	$131.70	$131.70
Purchase #7	$231.57	6.196%	$245.9181	$245.92	$245.90	$245.90
7 purchase totals =	$996.31		$1,079.8593	$1,079.86	$1,079.85	$1,079.90