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	$89.41	11.415%	$99.6162	$99.62	$99.60	$99.60
Purchase #2	$185.52	8.288%	$200.8959	$200.90	$200.90	$200.90
Purchase #3	$186.43	6.608%	$198.7493	$198.75	$198.75	$198.70
Purchase #4	$154.41	11.634%	$172.3741	$172.37	$172.35	$172.40
Purchase #5	$42.88	6.815%	$45.8023	$45.80	$45.80	$45.80
Purchase #6	$125.29	11.108%	$139.2072	$139.21	$139.20	$139.20
Purchase #7	$179.54	13.304%	$203.426	$203.43	$203.45	$203.40
7 purchase totals =	$963.48		$1,060.0710	$1,060.08	$1,060.05	$1,060.00