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	$68.59	13.565%	$77.8942	$77.89	$77.90	$77.90
Purchase #2	$153.93	8.550%	$167.091	$167.09	$167.10	$167.10
Purchase #3	$188.49	8.164%	$203.8783	$203.88	$203.90	$203.90
Purchase #4	$60.94	9.582%	$66.7793	$66.78	$66.80	$66.80
Purchase #5	$178.94	4.741%	$187.4235	$187.42	$187.40	$187.40
Purchase #6	$58.59	9.111%	$63.9281	$63.93	$63.95	$63.90
Purchase #7	$219.45	9.513%	$240.3263	$240.33	$240.35	$240.30
7 purchase totals =	$928.93		$1,007.3207	$1,007.32	$1,007.40	$1,007.30