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	$155.81	13.680%	$177.1248	$177.12	$177.10	$177.10
Purchase #2	$33.58	11.506%	$37.4437	$37.44	$37.45	$37.40
Purchase #3	$13.44	13.276%	$15.2243	$15.22	$15.20	$15.20
Purchase #4	$186.69	5.472%	$196.9057	$196.91	$196.90	$196.90
Purchase #5	$249.45	9.639%	$273.4945	$273.49	$273.50	$273.50
Purchase #6	$30.31	7.275%	$32.5151	$32.52	$32.50	$32.50
Purchase #7	$117.83	10.703%	$130.4413	$130.44	$130.45	$130.40
7 purchase totals =	$787.11		$863.1494	$863.14	$863.10	$863.00