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	$165.55	13.448%	$187.8132	$187.81	$187.80	$187.80
Purchase #2	$164.96	6.623%	$175.8853	$175.89	$175.90	$175.90
Purchase #3	$225.91	8.401%	$244.8887	$244.89	$244.90	$244.90
Purchase #4	$32.76	5.288%	$34.4923	$34.49	$34.50	$34.50
Purchase #5	$106.73	7.297%	$114.5181	$114.52	$114.50	$114.50
Purchase #6	$167.95	10.496%	$185.578	$185.58	$185.60	$185.60
Purchase #7	$64.64	9.408%	$70.7213	$70.72	$70.70	$70.70
7 purchase totals =	$928.50		$1,013.8969	$1,013.90	$1,013.90	$1,013.90