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	$139.46	11.459%	$155.4407	$155.44	$155.45	$155.40
Purchase #2	$80.51	11.194%	$89.5223	$89.52	$89.50	$89.50
Purchase #3	$150.28	13.357%	$170.3529	$170.35	$170.35	$170.40
Purchase #4	$83.94	7.573%	$90.2968	$90.30	$90.30	$90.30
Purchase #5	$153.32	9.528%	$167.9283	$167.93	$167.95	$167.90
Purchase #6	$30.96	6.151%	$32.8643	$32.86	$32.85	$32.90
Purchase #7	$98.49	11.500%	$109.8164	$109.82	$109.80	$109.80
7 purchase totals =	$736.96		$816.2217	$816.22	$816.20	$816.20