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	$246.75	6.297%	$262.2878	$262.29	$262.30	$262.30
Purchase #2	$90.65	9.659%	$99.4059	$99.41	$99.40	$99.40
Purchase #3	$87.75	10.791%	$97.2191	$97.22	$97.20	$97.20
Purchase #4	$84.28	5.545%	$88.9533	$88.95	$88.95	$89.00
Purchase #5	$124.41	5.711%	$131.5151	$131.52	$131.50	$131.50
Purchase #6	$48.28	9.425%	$52.8304	$52.83	$52.85	$52.80
Purchase #7	$32.99	12.564%	$37.1349	$37.13	$37.15	$37.10
7 purchase totals =	$715.11		$769.3465	$769.35	$769.35	$769.30