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	$100.71	3.399%	$104.1331	$104.13	$104.15	$104.10
Purchase #2	$55.69	13.395%	$63.1497	$63.15	$63.15	$63.10
Purchase #3	$139.48	4.138%	$145.2517	$145.25	$145.25	$145.30
Purchase #4	$182.55	3.132%	$188.2675	$188.27	$188.25	$188.30
Purchase #5	$67.34	10.602%	$74.4794	$74.48	$74.50	$74.50
Purchase #6	$49.48	3.245%	$51.0856	$51.09	$51.10	$51.10
Purchase #7	$82.72	8.699%	$89.9158	$89.92	$89.90	$89.90
7 purchase totals =	$677.97		$716.2828	$716.29	$716.30	$716.30