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	$178.99	6.756%	$191.0826	$191.08	$191.10	$191.10
Purchase #2	$127.88	11.508%	$142.5964	$142.60	$142.60	$142.60
Purchase #3	$206.76	13.317%	$234.2942	$234.29	$234.30	$234.30
Purchase #4	$106.53	12.582%	$119.9336	$119.93	$119.95	$119.90
Purchase #5	$76.82	8.634%	$83.4526	$83.45	$83.45	$83.50
Purchase #6	$238.94	13.345%	$270.8265	$270.83	$270.85	$270.80
Purchase #7	$41.65	8.244%	$45.0836	$45.08	$45.10	$45.10
7 purchase totals =	$977.57		$1,087.2695	$1,087.26	$1,087.35	$1,087.30