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	$226.77	10.191%	$249.8801	$249.88	$249.90	$249.90
Purchase #2	$80.73	9.507%	$88.405	$88.41	$88.40	$88.40
Purchase #3	$55.42	7.866%	$59.7793	$59.78	$59.80	$59.80
Purchase #4	$40.82	6.716%	$43.5615	$43.56	$43.55	$43.60
Purchase #5	$63.28	5.137%	$66.5307	$66.53	$66.55	$66.50
Purchase #6	$144.82	8.721%	$157.4498	$157.45	$157.45	$157.40
Purchase #7	$56.45	8.679%	$61.3493	$61.35	$61.35	$61.30
7 purchase totals =	$668.29		$726.9557	$726.96	$727.00	$726.90