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	6.442%	$139.8861	$139.89	$139.90	$139.90
Purchase #2	$134.78	9.524%	$147.6164	$147.62	$147.60	$147.60
Purchase #3	$50.94	8.597%	$55.3193	$55.32	$55.30	$55.30
Purchase #4	$237.45	5.584%	$250.7092	$250.71	$250.70	$250.70
Purchase #5	$152.49	13.836%	$173.5885	$173.59	$173.60	$173.60
Purchase #6	$240.25	11.646%	$268.2295	$268.23	$268.25	$268.20
Purchase #7	$44.29	4.715%	$46.3783	$46.38	$46.40	$46.40
7 purchase totals =	$991.62		$1,081.7273	$1,081.74	$1,081.75	$1,081.70