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	$145.31	13.770%	$165.3192	$165.32	$165.30	$165.30
Purchase #2	$82.90	9.593%	$90.8526	$90.85	$90.85	$90.90
Purchase #3	$228.82	13.696%	$260.1592	$260.16	$260.15	$260.20
Purchase #4	$130.79	13.663%	$148.6598	$148.66	$148.65	$148.70
Purchase #5	$176.77	12.450%	$198.7779	$198.78	$198.80	$198.80
Purchase #6	$196.35	11.593%	$219.1129	$219.11	$219.10	$219.10
Purchase #7	$230.31	8.856%	$250.7063	$250.71	$250.70	$250.70
7 purchase totals =	$1,191.25		$1,333.5879	$1,333.59	$1,333.55	$1,333.70