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	$100.85	10.173%	$111.1095	$111.11	$111.10	$111.10
Purchase #2	$50.95	9.720%	$55.9023	$55.90	$55.90	$55.90
Purchase #3	$86.88	4.848%	$91.0919	$91.09	$91.10	$91.10
Purchase #4	$23.25	7.871%	$25.08	$25.08	$25.10	$25.10
Purchase #5	$158.47	5.570%	$167.2968	$167.30	$167.30	$167.30
Purchase #6	$218.76	6.280%	$232.4981	$232.50	$232.50	$232.50
Purchase #7	$218.32	4.390%	$227.9042	$227.90	$227.90	$227.90
7 purchase totals =	$857.48		$910.8828	$910.88	$910.90	$910.90