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	$49.94	12.547%	$56.206	$56.21	$56.20	$56.20
Purchase #2	$29.49	13.831%	$33.5688	$33.57	$33.55	$33.60
Purchase #3	$238.91	4.323%	$249.2381	$249.24	$249.25	$249.20
Purchase #4	$168.73	12.354%	$189.5749	$189.57	$189.55	$189.60
Purchase #5	$100.72	13.802%	$114.6214	$114.62	$114.60	$114.60
Purchase #6	$127.74	12.622%	$143.8633	$143.86	$143.85	$143.90
Purchase #7	$89.82	11.731%	$100.3568	$100.36	$100.35	$100.40
7 purchase totals =	$805.35		$887.4293	$887.43	$887.35	$887.50