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	$75.43	3.581%	$78.1311	$78.13	$78.15	$78.10
Purchase #2	$93.59	12.855%	$105.621	$105.62	$105.60	$105.60
Purchase #3	$171.42	11.354%	$190.883	$190.88	$190.90	$190.90
Purchase #4	$152.94	9.205%	$167.0181	$167.02	$167.00	$167.00
Purchase #5	$250.64	11.318%	$279.0074	$279.01	$279.00	$279.00
Purchase #6	$22.78	13.469%	$25.8482	$25.85	$25.85	$25.80
Purchase #7	$63.96	11.390%	$71.245	$71.25	$71.25	$71.20
7 purchase totals =	$830.76		$917.7538	$917.76	$917.75	$917.60