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	$99.85	5.476%	$105.3178	$105.32	$105.30	$105.30
Purchase #2	$137.37	11.193%	$152.7458	$152.75	$152.75	$152.70
Purchase #3	$30.92	9.645%	$33.9022	$33.90	$33.90	$33.90
Purchase #4	$210.52	10.178%	$231.9467	$231.95	$231.95	$231.90
Purchase #5	$154.63	6.324%	$164.4088	$164.41	$164.40	$164.40
Purchase #6	$216.77	10.394%	$239.3011	$239.30	$239.30	$239.30
Purchase #7	$140.78	9.190%	$153.7177	$153.72	$153.70	$153.70
7 purchase totals =	$990.84		$1,081.3401	$1,081.35	$1,081.30	$1,081.20