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	$240.38	6.455%	$255.8965	$255.90	$255.90	$255.90
Purchase #2	$167.50	13.264%	$189.7172	$189.72	$189.70	$189.70
Purchase #3	$181.76	11.182%	$202.0844	$202.08	$202.10	$202.10
Purchase #4	$102.42	7.837%	$110.4467	$110.45	$110.45	$110.40
Purchase #5	$72.61	8.626%	$78.8733	$78.87	$78.85	$78.90
Purchase #6	$231.80	3.443%	$239.7809	$239.78	$239.80	$239.80
Purchase #7	$81.36	10.160%	$89.6262	$89.63	$89.65	$89.60
7 purchase totals =	$1,077.83		$1,166.4252	$1,166.43	$1,166.45	$1,166.40