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	$80.97	10.744%	$89.6694	$89.67	$89.65	$89.70
Purchase #2	$239.56	9.733%	$262.8764	$262.88	$262.90	$262.90
Purchase #3	$12.33	9.689%	$13.5247	$13.52	$13.50	$13.50
Purchase #4	$225.65	8.214%	$244.1849	$244.18	$244.20	$244.20
Purchase #5	$68.32	13.527%	$77.5616	$77.56	$77.55	$77.60
Purchase #6	$38.93	3.718%	$40.3774	$40.38	$40.40	$40.40
Purchase #7	$60.89	12.811%	$68.6906	$68.69	$68.70	$68.70
7 purchase totals =	$726.65		$796.8850	$796.88	$796.90	$797.00