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	$25.68	6.353%	$27.3115	$27.31	$27.30	$27.30
Purchase #2	$165.35	4.142%	$172.1988	$172.20	$172.20	$172.20
Purchase #3	$155.55	13.526%	$176.5897	$176.59	$176.60	$176.60
Purchase #4	$170.90	5.239%	$179.8535	$179.85	$179.85	$179.90
Purchase #5	$211.88	4.344%	$221.0841	$221.08	$221.10	$221.10
Purchase #6	$103.30	7.673%	$111.2262	$111.23	$111.25	$111.20
Purchase #7	$196.47	3.431%	$203.2109	$203.21	$203.20	$203.20
7 purchase totals =	$1,029.13		$1,091.4747	$1,091.47	$1,091.50	$1,091.50