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	$156.97	12.447%	$176.5081	$176.51	$176.50	$176.50
Purchase #2	$147.88	11.527%	$164.9261	$164.93	$164.95	$164.90
Purchase #3	$54.56	4.175%	$56.8379	$56.84	$56.85	$56.80
Purchase #4	$173.31	10.562%	$191.615	$191.62	$191.60	$191.60
Purchase #5	$54.40	3.133%	$56.1044	$56.10	$56.10	$56.10
Purchase #6	$145.72	12.821%	$164.4028	$164.40	$164.40	$164.40
Purchase #7	$98.88	4.279%	$103.1111	$103.11	$103.10	$103.10
7 purchase totals =	$831.72		$913.5054	$913.51	$913.50	$913.40