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	$131.42	4.443%	$137.259	$137.26	$137.25	$137.30
Purchase #2	$117.72	8.633%	$127.8828	$127.88	$127.90	$127.90
Purchase #3	$246.73	5.350%	$259.9301	$259.93	$259.95	$259.90
Purchase #4	$248.58	5.107%	$261.275	$261.28	$261.30	$261.30
Purchase #5	$198.81	12.315%	$223.2935	$223.29	$223.30	$223.30
Purchase #6	$47.78	13.826%	$54.3861	$54.39	$54.40	$54.40
Purchase #7	$250.83	11.572%	$279.856	$279.86	$279.85	$279.90
7 purchase totals =	$1,241.87		$1,343.8825	$1,343.89	$1,343.95	$1,344.00