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	$133.45	12.723%	$150.4288	$150.43	$150.45	$150.40
Purchase #2	$117.51	8.494%	$127.4913	$127.49	$127.50	$127.50
Purchase #3	$39.53	6.326%	$42.0307	$42.03	$42.05	$42.00
Purchase #4	$44.77	9.500%	$49.0232	$49.02	$49.00	$49.00
Purchase #5	$26.77	4.458%	$27.9634	$27.96	$27.95	$28.00
Purchase #6	$133.63	6.672%	$142.5458	$142.55	$142.55	$142.50
Purchase #7	$249.26	9.677%	$273.3809	$273.38	$273.40	$273.40
7 purchase totals =	$744.92		$812.8641	$812.86	$812.90	$812.80