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	$206.78	9.403%	$226.2235	$226.22	$226.20	$226.20
Purchase #2	$90.99	9.581%	$99.7078	$99.71	$99.70	$99.70
Purchase #3	$163.69	12.611%	$184.3329	$184.33	$184.35	$184.30
Purchase #4	$164.43	11.108%	$182.6949	$182.69	$182.70	$182.70
Purchase #5	$235.91	5.659%	$249.2601	$249.26	$249.25	$249.30
Purchase #6	$230.69	10.228%	$254.285	$254.29	$254.30	$254.30
Purchase #7	$92.29	12.334%	$103.673	$103.67	$103.65	$103.70
7 purchase totals =	$1,184.78		$1,300.1772	$1,300.17	$1,300.15	$1,300.20