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	$82.89	7.699%	$89.2717	$89.27	$89.25	$89.30
Purchase #2	$123.50	8.384%	$133.8542	$133.85	$133.85	$133.90
Purchase #3	$90.32	3.586%	$93.5589	$93.56	$93.55	$93.60
Purchase #4	$73.89	5.634%	$78.053	$78.05	$78.05	$78.10
Purchase #5	$219.36	9.360%	$239.8921	$239.89	$239.90	$239.90
Purchase #6	$119.64	5.707%	$126.4679	$126.47	$126.45	$126.50
Purchase #7	$52.37	13.260%	$59.3143	$59.31	$59.30	$59.30
7 purchase totals =	$761.97		$820.4121	$820.40	$820.35	$820.60