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	$74.43	11.681%	$83.1242	$83.12	$83.10	$83.10
Purchase #2	$232.85	3.195%	$240.2896	$240.29	$240.30	$240.30
Purchase #3	$97.40	3.209%	$100.5256	$100.53	$100.55	$100.50
Purchase #4	$235.49	5.323%	$248.0251	$248.03	$248.05	$248.00
Purchase #5	$242.88	5.530%	$256.3113	$256.31	$256.30	$256.30
Purchase #6	$217.98	10.288%	$240.4058	$240.41	$240.40	$240.40
Purchase #7	$99.61	6.683%	$106.2669	$106.27	$106.25	$106.30
7 purchase totals =	$1,200.64		$1,274.9485	$1,274.96	$1,274.95	$1,274.90