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	$163.36	11.163%	$181.5959	$181.60	$181.60	$181.60
Purchase #2	$44.39	12.712%	$50.0329	$50.03	$50.05	$50.00
Purchase #3	$141.60	11.256%	$157.5385	$157.54	$157.55	$157.50
Purchase #4	$186.56	4.362%	$194.6977	$194.70	$194.70	$194.70
Purchase #5	$26.33	12.386%	$29.5912	$29.59	$29.60	$29.60
Purchase #6	$89.39	5.817%	$94.5898	$94.59	$94.60	$94.60
Purchase #7	$82.89	9.592%	$90.8408	$90.84	$90.85	$90.80
7 purchase totals =	$734.52		$798.8868	$798.89	$798.95	$798.80