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	$104.75	11.750%	$117.0581	$117.06	$117.05	$117.10
Purchase #2	$21.85	11.694%	$24.4051	$24.41	$24.40	$24.40
Purchase #3	$194.37	12.531%	$218.7265	$218.73	$218.75	$218.70
Purchase #4	$229.74	10.600%	$254.0924	$254.09	$254.10	$254.10
Purchase #5	$85.66	4.530%	$89.5404	$89.54	$89.55	$89.50
Purchase #6	$24.30	4.499%	$25.3933	$25.39	$25.40	$25.40
Purchase #7	$65.25	3.257%	$67.3752	$67.38	$67.40	$67.40
7 purchase totals =	$725.92		$796.5910	$796.60	$796.65	$796.60