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	$38.67	3.759%	$40.1236	$40.12	$40.10	$40.10
Purchase #2	$59.80	3.119%	$61.6652	$61.67	$61.65	$61.70
Purchase #3	$174.85	12.273%	$196.3093	$196.31	$196.30	$196.30
Purchase #4	$59.27	9.290%	$64.7762	$64.78	$64.80	$64.80
Purchase #5	$37.83	6.296%	$40.2118	$40.21	$40.20	$40.20
Purchase #6	$108.34	5.527%	$114.328	$114.33	$114.35	$114.30
Purchase #7	$15.67	6.537%	$16.6943	$16.69	$16.70	$16.70
7 purchase totals =	$494.43		$534.1084	$534.11	$534.10	$534.10