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	$129.89	6.150%	$137.8782	$137.88	$137.90	$137.90
Purchase #2	$66.91	8.228%	$72.4154	$72.42	$72.40	$72.40
Purchase #3	$173.29	12.383%	$194.7485	$194.75	$194.75	$194.70
Purchase #4	$24.27	12.318%	$27.2596	$27.26	$27.25	$27.30
Purchase #5	$79.79	13.236%	$90.351	$90.35	$90.35	$90.40
Purchase #6	$92.38	12.874%	$104.273	$104.27	$104.25	$104.30
Purchase #7	$147.84	6.169%	$156.9602	$156.96	$156.95	$157.00
7 purchase totals =	$714.37		$783.8859	$783.89	$783.85	$784.00