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	$23.46	3.353%	$24.2466	$24.25	$24.25	$24.20
Purchase #2	$145.28	5.119%	$152.7169	$152.72	$152.70	$152.70
Purchase #3	$104.50	8.445%	$113.325	$113.33	$113.35	$113.30
Purchase #4	$162.43	7.569%	$174.7243	$174.72	$174.70	$174.70
Purchase #5	$118.82	10.258%	$131.0086	$131.01	$131.00	$131.00
Purchase #6	$16.86	12.382%	$18.9476	$18.95	$18.95	$18.90
Purchase #7	$134.38	3.815%	$139.5066	$139.51	$139.50	$139.50
7 purchase totals =	$705.73		$754.4756	$754.49	$754.45	$754.30