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	$129.73	8.297%	$140.4937	$140.49	$140.50	$140.50
Purchase #2	$59.35	7.698%	$63.9188	$63.92	$63.90	$63.90
Purchase #3	$48.81	13.726%	$55.5097	$55.51	$55.50	$55.50
Purchase #4	$115.55	13.213%	$130.8176	$130.82	$130.80	$130.80
Purchase #5	$91.86	9.836%	$100.8953	$100.90	$100.90	$100.90
Purchase #6	$236.25	5.691%	$249.695	$249.70	$249.70	$249.70
Purchase #7	$141.27	10.622%	$156.2757	$156.28	$156.30	$156.30
7 purchase totals =	$822.82		$897.6058	$897.62	$897.60	$897.60