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	$125.92	10.711%	$139.4073	$139.41	$139.40	$139.40
Purchase #2	$52.53	13.269%	$59.5002	$59.50	$59.50	$59.50
Purchase #3	$206.92	10.706%	$229.0729	$229.07	$229.05	$229.10
Purchase #4	$132.92	9.363%	$145.3653	$145.37	$145.35	$145.40
Purchase #5	$172.49	9.820%	$189.4285	$189.43	$189.45	$189.40
Purchase #6	$223.64	10.426%	$246.9567	$246.96	$246.95	$247.00
Purchase #7	$6.75	9.736%	$7.4072	$7.41	$7.40	$7.40
7 purchase totals =	$921.17		$1,017.1381	$1,017.15	$1,017.10	$1,017.20