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	$80.37	12.635%	$90.5247	$90.52	$90.50	$90.50
Purchase #2	$241.41	8.185%	$261.1694	$261.17	$261.15	$261.20
Purchase #3	$169.95	13.166%	$192.3256	$192.33	$192.35	$192.30
Purchase #4	$127.64	11.656%	$142.5177	$142.52	$142.50	$142.50
Purchase #5	$220.99	8.683%	$240.1786	$240.18	$240.20	$240.20
Purchase #6	$37.54	7.671%	$40.4197	$40.42	$40.40	$40.40
Purchase #7	$233.63	11.741%	$261.0605	$261.06	$261.05	$261.10
7 purchase totals =	$1,111.53		$1,228.1962	$1,228.20	$1,228.15	$1,228.20