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	$32.94	3.363%	$34.0478	$34.05	$34.05	$34.00
Purchase #2	$192.99	3.234%	$199.2313	$199.23	$199.25	$199.20
Purchase #3	$169.95	5.848%	$179.8887	$179.89	$179.90	$179.90
Purchase #4	$51.40	7.586%	$55.2992	$55.30	$55.30	$55.30
Purchase #5	$245.88	11.636%	$274.4906	$274.49	$274.50	$274.50
Purchase #6	$249.82	12.456%	$280.9376	$280.94	$280.95	$280.90
Purchase #7	$117.49	8.590%	$127.5824	$127.58	$127.60	$127.60
7 purchase totals =	$1,060.47		$1,151.4776	$1,151.48	$1,151.55	$1,151.40