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	$92.96	6.873%	$99.3491	$99.35	$99.35	$99.30
Purchase #2	$80.56	10.558%	$89.0655	$89.07	$89.05	$89.10
Purchase #3	$135.59	7.603%	$145.8989	$145.90	$145.90	$145.90
Purchase #4	$167.95	9.659%	$184.1723	$184.17	$184.15	$184.20
Purchase #5	$31.32	10.434%	$34.5879	$34.59	$34.60	$34.60
Purchase #6	$241.83	5.673%	$255.549	$255.55	$255.55	$255.50
Purchase #7	$119.69	7.672%	$128.8726	$128.87	$128.85	$128.90
7 purchase totals =	$869.90		$937.4953	$937.50	$937.45	$937.50